How do I go about reporting someone for something that happened outside of the game (cs or postchat)

I tried to screen shot something someone said in champ select but i messed up and then the games started but I did manage to copy paste it... I remember riot said they are able to go into champ select chats and see what was written, I'm usually not too flustered about toxic players in my game but this person... is just... really something. I need to at least try to do something about it so I can sleep well tonight. (I did report them after the game for several things, which they will most likely get punished for but the real crime was the champ select)