It needs to be leveled (the whole area of surrounding frets....you cant just work on one fret) then crowned and polished. Sorry, but that's it. Replacing just the one fret will still mean you have to level, crown and polish the surrounding frets after replacement anyway. Usually a ding is cause by a string being knocked against a fret. In the case of SS wire that ding would not be very deep, so it wouldn't take much levelling.