I've seen some claims that it is as simple as doing the same thing one would do when breaking it in originally.
Depends on the glove and the quality of leather.......even if it can't be corrected 100%, it can be made better. But again, just depends?
I'd just place a ball in it, always, when not in use; and make sure it's wrapped in the position it needs to be with rubber bands/bungee straps. Also put conditioner/oil on it where the shape needs to change.