If you suspect another member of using disallowed resources, 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. If you would like to discuss, join the following club: https://www.chess.com/club/cheating-forum
j'ai un utilisateur discord qui prétend être passé de débutant au échecs "1200 elo" à 2000 elo en 2 mois, comment voir si il triche ?