The technical error is rarely the problem. The problem is the 20 seconds after: You look at the bench, you judge yourself, you're not in the game. And because you're not in the game, the next mistake happens.
Why a gesture works better than a thought
"Don't think about it" doesn't work – the phrase itself contains what you're trying not to think about. A physical action, though, is clear: grab your shirt, breathe out, say a word, look forward. Your mind gets a task instead of a ban.
Practise it where it's cheap
Use the routine in training after every misplaced pass. After two to three weeks, it will run automatically – and then it will also work in a cup game.