If you get angry at anything, generally the best thing to do is to walk away.
If it keeps happening, just stop what makes you angry indefinitely. Make no plans to do it again. If it happens you do do it again, generally will notice a much more calm approach.
Contrary to most people, I do get the reasoning behind taking the game seriously and getting better and competing, and i also don't consider it a waste of time. It's a good way to spend time. So i do understand reluctance to quit doing something that makes you angry if it also makes you happy.
Other than that, meditation and self reflection are the best ways to understand why you are angry, and consider if it's valid.
Most of the advice people give is all the same stuff. It's usually correct too. So if you know the advice, and remember it, whether or not you listen and take it on board is on you, noone else.
I only type this because I'm known for being similar. Angry for no real reason. Was mostly tied to my real life and I'd bring it out online as a venting system. Fixing most of that let me take the time to think about emotions in a different way, and calmed me down a lot. I'm still loud and annoying to a lot of people, and I still get mad at losing but it's the good kind of anger that makes you want to play more and prove more, rather than just getting angry at others. Fixing the anger issues won't make you nicer, it won't make more people like you, and it won't change who you are. So if those are your aims, fix it them elsewhere.