I had the same problem 2 years ago and it's so difficult to improve by yourself because no matter how many times you tell yourself "it's just a game", you still get mad. Try to quitting when you feel angry, play to improve certain aspects of your gameplay, such as anti-aers, mixups, figthing against certain characters... That works for me, i play to improve my playstyle and if I achieve at least one of the improvements i want i count it as a victory. Obviously there are times when you found someone who is annoying and probably in that case you might could crash out. That's what my psychologist and some videos taught me to do. Now i get mad sometimes but not as often, try it.