The best thing to do is to make a past of a few different things. powdered comet dishwashing detergent baking powder and some bicabonate soda for a phissing action.
seltzer water is a bicarbonate soda.
You want to get the stuff to come of of the other things by letting it soak in. DO NOT use any hot water, cold water will remove the stains the fastest and will not set the stain!! Make a thick past and if you have it a citrus claner to the mixture will doo fine as well. The important thing here is to get the oxygen to bubble up somthing like oxy clean will have the best result.