You can freeze mashed red potatoes. To freeze the potatoes, you can place individual scoops on a sheet pan, and then store the frozen scoops in an airtight container. To reheat, thaw the scoops in a refrigerator and then microwave them until hot, about 2-3 minutes per scoop. Stir the potatoes occasionally for even heating. You can also freeze mashed potatoes as a single batch in a container. To reheat a batch of mashed potatoes, thaw them in a refrigerator. Then put them in a covered baking container and reheat them at 350 degrees F until hot, about 20-30 minutes. You should stir the potatoes to make sure they are evenly heated.