where do i report someone who i think is getting boosted

so I ran into a guy in my game who absolutely stomped the shit out of me, froze lane towerdived, ended the game like 25/2 i normally do fairly well as a laner in bronze since ive been in silver promos a few times so i thought he was a smurf and decided to look into it, turns out his op.gg hes like b4 35% winrate over the season but his last 20 games in the lol client profile viewer have all been 20/0 as fizz and kat even tho his most played ranked champs are like jungler with a 20-40% winrate