This section of IGN’s Little Nightmares 2 wiki guide will walk you through the chess puzzle. Solving this puzzle will give you the key to open the door on the first floor of the School.
When you reach the door on the right, put the top on the white rook to make a platform to stand on. Then, jump to the handle to open the door. This will lead you into a room with a strange, broken chessboard on the ground, including one of the Bullies as a piece.
Continue heading right and you’ll see a picture with a red eye drawn on it. Jump up and pull the bottom to reveal the key to solving this game of chess. You need to find the tops to the missing pieces and put them in the correct spot. Head to the right to find the queen, the king is on the table to the left of the board, and the rook is on the piece outside of this room.
In order to reach the king, just place the rook piece in the queen’s spot temporarily. That way, you can climb on top of it to reach the table, then put it back once you’ve got it.
Once everything’s on, a light will flicker on your right. Jump over to it via the top of the rook and pull down on the light. This will open a secret door where you’ll find the key.
Now, grab the key and head back downstairs to unlock the door.