I have had geographic tongue for the last 10 years and I have found 2 things that help. When cooking grains and beans I soak 1 cup of grains (rice, millet, etc. ) in water with 2 tablespoons of apple cider vinegar for 12-24 hours helps to remove the phytic acid and make it easier to digest, and separately 1 cup of beans (any legume) in water with a teaspoon of baking soda for 12-24 hours before cooking. I ran across this suggestion and thought that I would try it for general health and after 1 week of this I noticed that my tongue was feeling about 20-30% better.
About 1 month later I also started drinking 2 tablespoons of unpasturized apple cider vinegar in 16 oz. Of water throughout the day, again for general health, and found that after 1 month my tongue was about 90-95% better. If you use a weaker solution it might just take longer to see results, but if that is what it takes to make it palitable then go for it. It seems counterintuitive to drink ACV for geographic tongue because the acid makes your tongue burn a little bit, but if you stick with it then you should see an improvement. Other things that help me are cutting out coffee and wine from my diet.