This is from the walkthrough:
Window: Check the window in front of the right projector. Slide the cover off using the handle and see that window is dirty.
In inventory, use the spray bottle on paper towel to get soaked towel. Use soaked towel on dirty window.
So - face the projector closest to you when you just come in the room.
There is a window that is in front of that on the wall to your right.
Slide the cover and see that the glass of that window is dirty.
Clean it then.
