Friends account has been hacked and username has been changed

My friends account has been hacked recently (he hasn't had access to it in over 3 months at this point) the name was changed to "Kinky uwu" by whoever has hacked it and been playing on his account since. His username was formerly "Rivaldmans" and he has been a top tryndamere/shyvana main for almost 6 years by now and this person has played almost only Cass in mid for the last several months. with the new changes to the launcher neither him or i know how he could regain access to his account and change his name back without paying money for a summoner name change. they have made purchases on his account recently and that is why he is in urgent need to get his account back. if anyone could give any information as to how he can regain his account and revert the name change, I would be greatly appreciative. I have linked the OP.gg for the account in question