This section of IGN’s Little Nightmares 2 wiki guide will walk you through chess puzzle. Solving this puzzle will give you the key to open the door to the first floor of school.
When you reach the door on the right, place the top on the white tower to make a platform for you to stand on. Then jump on the handle to open the door. This will take you to a room with a weird, broken chess board on the floor, including one of the Bullies as a room.
Continue to the right and you will see an image with a red eye drawn on it. Jump and pull the bottom to reveal the key to solving this chess game. You have to find the tops of the missing pieces and place them in the right place. Head to the right to find the queen, the king is on the table to the left of the board, and the tower is on the room outside of that room.
To reach the king, simply place the tower in place of the queen temporarily. This way you can climb over it to reach the table and then put it back on once you have it.
Once everything is on, a light will flash on your right. Jump there via the top of the tower and shoot the light. This will open a secret door where you will find the key.
Now take the key and go back down to unlock the door.