Climb the ladder.

Remove the screws of the securing bracket with the philips head screwdriver.

Tap and turn the securing bracket to remove the lock.

Open the door and go to the second floor.

Enlarge the metal shelf mounted on the wall of the second floor.

Remove the screws at the four corners with the philips head screwdriver and open the cover.

Find the missing plate.

The shape coincides with the plate mark of the box on the floor.

Press all the drawn patterns and press the right button last.

Press the switch on the box and get the iron box from inside.

If you open the elevator door and peer downwards, a dialog box with the message "Should I jump down?" appears BAD END results if you press "Yes" and jump down.
※You can start all over again from the previous step without the saved data disappearing.