First try laying ice cubes in a zipper type bag ontop and leave there a few minutes. Then scraping with the edge of a knife. If not:

1. Sponge with a small amount of dry cleaning solvent

2. Blot

3. Mix one teaspoon of a mild ph balanced detergent (a mild non alkaline non bleaching detergent) with a cup of lukewarm water

4. Blot