I’ve had a few damaged DVDs over the years. First thing to try is, obviously, gentle cleaning with a soft cloth, which sometimes works, especially if combined with a spray of IPA to remove oils and greases. Or on a lower budget, a puff of breath polished off on your shirt sleeve often fixes things.
Otherwise, if the disc resists and there’s nothing to lose, I’ve resorted to more aggressive tactics, including toothpaste and abrasive polishes. They rarely do any good but interestingly, they rarely make things worse either.
I’ve even tried wet-sanding with fine-grade abrasive paper until the disc surface was completely hazed, followed by polishing with a cutting compound until it was shiny again. That certainly wasn’t a cure as the disc still struggled, but it didn’t seem to do any further harm either.