Hey! Yes I can understand this and it’s something I have also struggled with in the past too, many players do. I think the best thing is to try and have a clear plan in your own game and the way you play, this helps you go into each match with a certain way of playing and of course you adapt this depending on your opponent but it helps you play with a more clear mind.
I think it’s also important to stay focused on these tactics during a game and not think about the outcome as this is where stress and frustration can kick in. Focus on one point at a time, you can’t change the past but you can change the future by being positive and calm.
Lastly I think it’s really important to try to find a way to enjoy matches, this makes in much easier play your best and keep improving. Let us know how you go!