Pour 1 cup of distilled white vinegar and 1 cup of warm water into the skillet. Add 1 tablespoon of baking soda. If the mixture does not cover the blueberry stains, add more water and vinegar.
Set the skillet on the stove and turn on the heat. Let the mixture reach a boil. Keep the skillet at a rolling boil for 20 minutes. Turn off the heat, carefully pour out the liquid, and rinse the pan with warm water.
Sprinkle baking soda over the bottom of the skillet. Scrub the baking soda over the stains with a scrub brush.
Fill the skillet with water. Add a denture tablet to the water. After the tablet stops fizzing, empty the water, and rinse the skillet. The tablet removes any stains that were left behind.
Cover a washcloth with a thin layer of baking soda. Spray stains on the outside of the skillet with either distilled white vinegar or plain water. Scrub the stains with the cloth. Rinse the skillet, and dry it or let it air-dry.