Hi Leo. I'd recommend playing slower games. If you are playing 3 minutes or 5 minute games, maybe try playing 15/10 instead.
How do I stay calm during a game?

Play more so you get used to it
+1 Nothing helps like playing experience; everyone was once a beginner. Another tip to help play slower and be less nervous is to literally sit on your hands. It is an old trick. The act of needing to move your hands out from under you before you move will remind you to do a "blunder check." Double check once more to see if you overlooked something like a hanging piece or a new threat. This time may also remind you to look for a better move or enjoy the moment of the chess game, rather than to get "too into" the game. The best chess players are the somewhat relaxed ones because they are free to think creatively about the position; try to have fun and you will indirectly play better in most cases

I think you should knock down a Corona or two before each game. (I am talking about beer). That will relax you for sure. After about 5-6 games you will Most likely be sleeping like a baby.

What are some tips to stay calm?
Focus on the job and not on what may happen if you don't do it right.

I remember having this exact problem during a high school tournament game, I was so focused on the clock that my opponent had me rolled up and smoked before the middle game got underway. My chess teacher reminded me it didn't matter how much time was left on the clock if you lost. He then went on to tell me it is far better to lose because you ran out of time than it is to lose because of blunders that you made because you were focused on the clock and not the board. Since then I've played plenty of games on the clock but I've never lost solely because of time trouble. I hope this helps
Play more.
If you play a lot of games you stop caring about time or losing or losing badly or hanging the queen or about rating. It gets to the point it's all just one more game, after all.

I think you should knock down a Corona or two before each game. (I am talking about beer). That will relax you for sure. After about 5-6 games you will Most likely be sleeping like a baby.
Week nights are peppermint and chamomile teas for me.
The whiskey bottles comes out on the weekends.
Works for me.
Hi!
You have to remember that chess is a game played for fun, what is the worst thing that could happen if you make a mistake, lose a game? Big deal, I’ve lost thousands, and nobody ever got hurt from my bad moves. It’s just a game! Review the game afterwards and figure out what you did wrong and what was the right idea(s).
-Jordan

To keep it 'all in perspective'
some of us just take a break from time to time
from playing Rated Matches and
kickback and enjoy UNrated casual stress free games such as:
https://www.chess.com/club/unrated-relaxed-casual-usa-play

Leo - I find, when I am in the mood to do so, that playing an UNrated match is just plain relaxing and not one, whereby, I feel nervousnous, e.g., - https://www.chess.com/club/unrated-relaxed-casual-usa-play Sam.

One thing is focusing on breathing for just a few seconds. I take three slow deep breaths and just think about breathing for a moment. Another breathing exercise is a double inhale and a slow exhale. There's a lot of science behind the double inhale process - documented in the 1930s and recently talked about by Huberman. Once I get excited in a game, I get tunnel focused and miss things 1000 miles away on the other side of the board. :-)
PS - The double inhale - how it works - Take a basically regular breath, and then pause for a moment, and take just another breath on top of that. Then the slow exhale gets rid of more CO2 than usual. FYI.

Stay with the chess calculation so you do not get distracted by fear and its derivatives.
If you stay with the calculation, you will see that all chess is is trying to find the best move from the current position on the board - regardless from the fact whether that position is winning or losing. And if you struggle with time, use it strategically and plan your move in time so you don't run out. Don't be afraid to lose, if you do the above you will lose less and less. Losing is necessary for the learning process. Another day in the office, to quote Botez.

The more you think the game matters, the more stressed you will be. Hint: "the game" - it is A Game. If it were my job or life, I would play d4, Caro Kann, and would always answer d4 with d5. But it is Not.
"Chess is my life, but my life is not chess" - Anatoly Karpov.
Being nervous isn't necessarily a bad thing. It can keep you alert if it's proportional, which can increase your chances of winning.
* If it's not proportional, then that means that you think chess is important. You need to find meaning. Go to India, search for yourself. When you have something Much more important than chess in your life, you won't get so stressed in chess. One of the problems today is that we forget about what's important in life - the afterlife. *This* life is super stupid. Make sure you have an after-life, then nothing can stress you all that much - same psychology - If you think (or know for sure) that there's something more important than what you're dealing with, so what you're dealing with isn't so stressing.

try to forgot everything you had did just focus about chess even if it is a bad day
If you stress there are high chances to lose but if you are calm you have more chances to win even if they were 300 or 400 elo higher than you i know you wont believe me but my rating doesnt make sense to my real ratings
Real rating= 1450
chess.com rating=500 and it doest even make any sense
so when i calm down i can beat these really high elo people.
there used to be a hole in the facing wall to my computer stand that's where my wireless mousses went when i blew up i tried attached mousses and the chord could reach the hole so i could retrieve them but usually after three or four times they didn't work -- then i fixed the hole and got a laptop and double sided taped it to the desk i play at -- now no more tension
but now i need to fix the chair now every once in a while the back keeps loosening from slaming against it .its much less now but every once in a while and i don't play in bed chess that is those med naps make forget where i put the laptop when i doze off and then when i wake up - i don't see it under me or at the end of the bed -- then its off tp the computor store to see what the upgrades will cost me
What are some tips to stay calm?