In the 2nd room of Sector 4 you need to use 2 blue cubes to get to a higher ground. Instead of walking towards the next room, turn around when you reached the top and jump on the ledge on the right of you. Walk towards the hole in the wall there. You will get thrown into the room with the hidden puzzle.
See below video on how to solve it. (Credit goes out to “Hantu Vision” for uploading this video)