Idk what to do with this one rito

I can't post screenshots due to the privacy rules on the board but how do I report someone if I'm suspicious that they were literally boosted? I'm not trying to bm at all, I played a ranked game yesterday and my top lane turbo fed so I looked at his profile, he was in plat, looked at his match history, and he had previously played probably around 90% of his games on one champ and was POPPING OFF, and then he gets to my game, plays a different champ randomly, builds them in a bizarre manner, and turbo feeds.

I'm not trying to bm, I get that people have bad games but this one just seems a little suspicious to me.