I wanna reform

If somebody's being really relentless, mute them. That's always good advice. Rather than responding to anger with anger in return, try to respond with calm. Be aware of your own agitation but choose to exercise self-control. "I can't stop myself from flaming" is no more true than, "I can't stop myself from feeding the enemy team." The fact is, if you can do one, you can do the other -- and you should strive to do both. Acknowledge your negative emotions, acknowledge your struggle, but respond with positive sincerity.

"I'm sorry that I'm playing badly. I'm struggling and on tilt. Flaming me will not make things better. If you have any constructive suggestions, I would appreciate the help."

It will not always work. Nonetheless, it is always a better response to somebody flaming you than flaming back. It's mature, polite, self-aware, and sets the tone for a productive, cooperative game. Your humble response has the potential to deescalate a tense situation. An agitated response never will.

The common response to this suggestion is, "It doesn't work. Trolls gonna troll." Perhaps. Nonetheless, there are fewer trolls and fewer implacable flamers than you believe. You cannot discern the trolls and the flamers from reconcilable team mates without attempting to deescalate.

I said about impossible, not impossible. If you try and troll, of course you will be banned, but that's a conscious effort on your part to try and be banned. Typing is usually a reaction, so that's what he needs to cut out to be reformed.