1. Press on the ground on the bottom right corner above the word "FLOOR". See the next picture to see the spot.
2. Pick up the green knob in the hole in the ground and put it onto the left hole on the door.
3. Turn the left green knob to face 9 o'clock and turn the right green knob to face 4 o'clock. A panel should open with a lever in it. (see above picture)
4. Select the lever in your inventory and put it next to the wall on the right side. (see above picture)
5. While pressing and holding the lever, press the green arrow. Proceed to the next floor!