archivist2, welcome to RP.
i had a go at your image. a difficult one. i started with 'fade correction' in psp. then did a histogram adjustment. after that, i added a blank layer and filled it with a 128/128/128 gray fill. on this, i used the lighten/darken tool to adjust the various lights and darks that were amiss. after that, i used airbrush for even more contrasting, particularly added more dark to the darks and getting rid of some of the underexposed artifacting. cloning and push followed that to smooth things out a bit and do some solids where needed. there was a lot of this and some of the fine detail was handled with the push brush. near the finish, i added a hue/sat layer to get rid of some errant color junk. and that was pretty much it.
there is more that could be done, depending on what you consider might have been damaged and what was there to begin with.
the hardest part was the gentlemen in the middle, sitting, and the one behind him. these could, perhaps, also be done better with some rebuilding.