If you feel another member was using disallowed resources you should report them.
https://support.chess.com/en/articles/8562517-how-do-i-report-someone
That said, discussions of cheating, potential cheating, or cheat detection are not allowed in the general forums
I played a cheater today.
I want to bully low rated players in open challenges and I played a 500 rated player who played better than me (I am rated 1200). I then game reviewed and he got 96% accuracy and 1650 Elo prediction.