Presumably we don't need to sharpen the wing feathers of a Skarmory, yes? Since they moult naturally on a fairly regular basis? (How in Johto DO I groom my Skarmory, anyway? Should I even do so? He doesn't seem to appreciate my efforts - far from it - and spends plenty of time preening and keeping himself pretty tidy.)
The preening process is their way of polishing and sharpening their feathers! I really don’t recommend for trainers trying to sharpen them themselves because they’re just so sharp and there’s just… so many to try and avoid while you work.
In general, Skarmory handle their own grooming pretty well. But in some circumstances if rust buildup is too much for them to deal with on their own, you have to go in with a scrubbing pad and a cleanser.
With well-trained Skarmory this isn’t typically an issue for most professional groomers. It’s just a matter of keeping the wing straight and immobile and being very aware of the edges as you separate out individual feathers. I’ve even seen some groomers have the Skarmory rest on their backs or stomachs to work with the feathers against a flat surface but I’m not sure how many Skarmory are trained to tolerate laying down for that long.
Basically– please don’t, just keep your Skarmory out of the water and if accidents happen, dry them off as fast as possible with towels or even fans if necessary.