Looking at a collection of your games is a good start. How are you losing? Do you blunder material? Get squeezed to death? Do you lose in the opening, middlegame, or endgame? Do your mistakes come when your position is better, or when it's worse?
Depending on the answer, there are various approaches. If you miss a lot of tactics, intelligent use of Tactics Trainer can really help. Don't just eat tactics like peanuts--when you miss one, carefully study it and try to figure out the principle behind it. (This is how I found out I miss the tactic where you sack your queen then knight-fork to get it back--once I worked on that, I won two tournament games in a row with it.)
If you are bad at endgames, endgame drills are similarly helpful. I recommend starting with R+P and K+P as they are common and fundamental.
If you lose to openings, look at master games in your opening of choice, try to see where they put their pieces for a given pawn structure and what pawn breaks they use. Videos on your opening can also really help here.
Hello. I'm around 1600 on lichess rapid. How do I determine my weaknesses in chess? Then once I know what my weaknesses are, how can I work on them?