Think of a game that doesn't make you toxic and play with that same sort of mindset(like idk flag football or chess). And if you're going to type something that shifts the blame, don't do it. Farm up, buy items, secure objectives. If you type something, make sure its for the benefit of the team(i.e. asking for assistance, making a strategy over baron, calling ult times). Avoid comments that make you or your team feel bad. They are probably as frustrated as you are depending on the stage of the game.
Breathe evenly to keep a level head. Remember its a game and you are meant to have fun.