One strategy: lots of praise when you see the attitude you want to see. Not praise for finishing the task but praise if you catch them shaking something off or giving up but then going back to something. And pointing out, casually and positively, when you see that behavior in others. “Looked like Alex really got frustrated at baseball today. Did you see him throw his glove? That wasn’t cool. But I was impressed that he really calmed down after the coach talked to him and went back in there and pitched the third inning.”
Kids definitely can change. One of mine was pretty painfully shy and hesitant to do hard things. We tried not to put pressure on to be our idealized child but gave lots of opportunities to succeed and grow confidence while we maintained just kind of quiet, confident expectations that he’d be able to do xyz things we knew he was capable of, praised when he succeeded, and calmly said “yeah, that was hard, huh? You’ll get it next time” when he didn’t. By high school, he was like a different kid d - still can be slow to warm but confidently advocating for himself in all kinds of situations and taking on hard tasks to challenge himself. I think the equivalent for an easy to anger kid would be still having those emotions, but recognizing them and shaking them off and moving on. I’d work on those skills rather than thinking about it as trying to change his personality.