To remove scratches, use Scotchbrite pads.
These are synthetic "sanding and polishing" pads sold in automotive stores for use during painting a car.
Select one that most closely matches the guns original grained finish and rub the scratches until they're gone, or at least blended in with the rest of the gun.
To finish off, "stroke" the pad in the same direction the original grain runs.
To shine up, use any good stainless polish, like Mother's Mag polish, MAAS, Flitz, or any other.
Do not use the pads or the polish on the areas of the gun that have a bead blasted finish, like the top of the frame.
The only way to re-do those areas is by re-bead blasting them.
DO NOT use steel wool on a stainless gun to remove scratches.
The steel wool will embed tiny particles into the stainless.
Later the mild steel particles will rust, damaging the stainless.