reporting a troll

so i was in ranked champs select and our first pick said he was going to troll because he gets trolls and feeders in his games we tried to to reason with him and calm him down but with no success , when he locked in {{champion:16}} with {{summoner:6}} {{summoner:1}} (i was the support anyways) we started to argue on who should dodge and save us from this guy , i decided to dodge and said that i took a screenshot of this and am sending it to riot , then he said : "WTF" then he dodged the only way i tp report someone i know of is the post game results where you can honer/report someone etc .. so does anyone know how to report this guy and send the screen shot to riot ? , in case someone asks me about the screenshot i dont have it on the pc am using now , i was playing in a pc cafe at the time but i can get it later
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