Player admits to intentionally throwing his placement games. Wants his account at Bronze 5.

A player in my ranked game pretended to be new to Ranked and his role. Said he normally plays ARAM and it's his first time ADC. Proceeds to intentionally die through out the game. We don't look much into it because we just think he's a really bad player. I add him after the game to give him advice on how to play. He admits that he lost the game on purpose and is trying to get his account to Bronze 5.

I wasn't able to report him in game because I thought he was just new. Is my only option outside of game to send a ticket to riot? There's not even a report option. When I tried sending a ticket, there was no where for me to put the images to give them proof. Can someone help me properly report this guy?