Restoring a stainless piece is a series of steps.
Hammer out the dents
use a file to bring the piece back to perfect shape
sand the piece with progressively finer paper
buff to the final shine with stainless compound and jewelers rouge
A grinder might work in a pinch, but a larger 1/3 to 1/2 hp motor makes for much better buffing. You need eye protection, usually a full face shield. You also need leather gloves because 1) the metal gets extremely hot, and 2) the pieces can get ripped out of your hands. If your attention slips, the wheel can grab the stainless and the trim becomes a sword or spear in a nanosecond.
Restoring stainless or aluminum trim is not rocket science, but it is dirty, time-consuming, and extremely hard on the back and neck. If you have some experience doing hammer & dolly bodywork, it is a lot the same, just on a smaller scale.