Normally stainless steel is polished with buffing wheels and buffing soap, ( there is also electrolytic polishing, but not practical for home use ) but for your application it depends on the type of scratches and where they are, small ones could be removed with a Dremel type tool with the right buffing attachment, if there are a lot over a large surface it best to have it done on a big ( about 8" dia ) wheel professionally.