How to manage tilt?

So I'm in bronze one promos, I was playing support and early game we got a 26-10 lead and 2 dragons. I was fed and everything was going well, until teamfight phase. Our nasus top was farming when we teamfight, and Ivern does not tank damage... eventually the game hits the 40 minute mark, our advantage became less decisive and we ended up losing the match. I felt so tilted afterwards that my team has no sense of pushing;baiting objectives;teamfights, and became so tilted. But I'm not here to rant about bad teammates and stuff, I just would like your advice, how do you guys manage your rage and not let your anger carry on to the next few games?