It's like I forgot how to play chess
Improving Your Chess - Resources for Beginners and Beyond.....
https://www.chess.com/blog/RussBell/improving-your-chess-resources-for-beginners-and-beyond
Sometimes it really feels like chess disappears for a while, especially during a long losing streak. Dropping from 500 to 300 can happen quickly when a few habits slip and then confidence also starts to take a hit.
What usually helps is slowing the whole game down for a bit, even in simple positions. Before every move just checking what the opponent is threatening often brings a lot of rating back quite fast, because most losses at this level come from immediate blunders rather than deep strategy.
It can also help to temporarily focus less on results and more on just playing a few clean games in a row where the goal is simply not to hang pieces.
Have you noticed whether the blunders are happening from one specific pattern, like missing checks, or is it more random in your games?