[Hanschri]

You don't even have to relay the move to the player, simply giving a sign that this move is important can be enough for the player to understand they've got the edge and utilize that. It could be as simple as someone in view giving a sign with body language. Remember also that a professional chess player doesn't need to cheat every single move, cheating once in a game at the right move can be enough to put the game in your favor at such a high level.