what should I do?
Check him/her.
just play on. it will impossible after while
Maybe try 1 e4 e5 2 Nf3 Nf6 3 Nc3 Nc6 4 Bb5 Bb4 5 O-O O-O 6 d3 d6 7 Bg5 Bg4 8 Bxf6 Bxf3 9 Qxf3 Qxf6 10 Qxf6 gxf6 11 Nd5. lichess.org/forum/general-chess-discussion/how-to-beat-a-copycat
Remind him of the copyright!
check then move all pieces.