it already is, someone just made it all white except the blacked out windows.
What is it your asking for? Your description is vague. Do you need the lightmap fixed or a mesh built? Sounds like that light map is backwards. All you need do is select the white area, make it a color like blue by filling in. Reason is because if you made it black, your entire map would be black and your windows will be gone. Then do an invert select, and max the brightness for the windows making them white. Hit invert select again and fill in the blue with black.
If your asking something else then just disregard all that