1. Use the UV flashlight on the upper left corner to see the first clue.
2. Now use it on the upper right corner to see the second clue.
3. Tilt your phone to the right so the rock slides to the right side. Then slide your phone slightly to the left so the 2 balls move to the left side of the room (while the rock stays on the right side).
4. The door should be unlocked. Press the door to open it.