Fogging windows is something every LD owner can look forward to if they keep their rig long enough.
Few shops specialize in repairing or replacing fogged glass.I know no one who has a successful repair that has lasted or didn't suffer damage to the paint around the window. This doesn't mean that a satisfactory repair can't be made, I know of no positive examples.
If any member has had a good experience, lets us know. We also have fogged windows that need repair.
The windows can be removed without damage if care is taken to mask around the perimeter of the window frames with multiple layers of masking or duct tape. It takes time to get one free without damage.
Your choices are to use a shop that does the entire job or remove the window yourself and send it to a shop.
The glass can be defogged or a replacement insulated glass panel fabricated.
Lazy Daze can replace the complete window, it's an expensive alternative.
Here's kit to clean the glass in place. I have no idea how well it works.
Larry