It's about maturity and self-control. No, that's not an insult, I'm just saying those are two paradigms that you can improve over time with practice and patience. The fact that you care and are trying to improve is enough to prove you have the potential to grow in this aspect. Considering that several adults are incapable of this, including senior citizens, you should feel accomplished in this regard.
Now, as for alleviating behaviors...
Standard procedure is mute all if necessary (not at the start of the game, but when you hit that breaking point IMMEDIATELY mute everyone and rely on pings). Instead of typing when you feel angry, try yelling at the screen verbally. When your throat gets sore and you feel bored by yelling the same things, you'll eventually tire and stop it and this might translate to your games.
De-stress after games. Always important.
Shake things up and remember to play normal games. Play roles you aren't used to, champions fun to play but you're not skilled enough with or the meta doesn't favor them in competitive.
Play support occasionally. You might develop paternal/maternal instincts that help you keep your tilting moods internal in fear of hurting your beloved demon spawn.
etc etc
