to build a stronger mind

Everyone who compete focus on tecnique and focus on training their body, strenght, cardio etc.
Those things are very important in competition but we don’t have to forget that there is a huge psychological part in a fight and that part sometimes determine who win or who loose.
To have a strong mind is very very important for a fighter, think about a fighter that is very good tecnically, very fit and strong.he goes to the mat or to the ring and suddenly became scared and can’t play his game, all his effort on technique and strength are gone because of his weack mind.fear play a big role in competition and can make you loose.
I met one guy that even if he competed many times before, he was so nervous before a judo tournament that he threw up and wasn’t able to compete that day.
So do you guys know a way to train your mind/character ?
It’s a so important part of the game but I think that not many people focus on it.
To be onest I don’t know how to be stronger mentally, what to do etc.
The only way that I know is compete, I think that the more competition that you do the more mentally stronger you become.
Do you guys agree ? do you guys have other idea to become stronger mentaly ?