Sure, okay so when you go to the bathroom, you need to keep investigating when prompted. A series of numbers will flash on the screen.
Later you need to go to the floors corresponding to these numbers in that order using the elevator in the lift lobby
Once done a phrase will flash across the screen that tells you a clue which theatres to enter and how many times in order to unlock Theatre 6
If this is still unclear, I can tell you the exact answer straight away but I'll let you try first. Once you finish meeting the Killer in Theatre 6, the movie options for the couple will change to the True End options and youl'll be on the right path