This is a sign of poor health or poor diet.
Stop sugar intake. No sugary beverages and only whole fruit, no juice. Cleans the mouth and brush the tongue using neem toothpaste once a day and baking soda toothpaste the other 2-3 times a day, brushing the tongue every time. Drink green tea with mint every day, unsweetened. Stash makes a wonderful mint tea called Moroccan Mint.
Eat lots of vegetables every day and lean meat the size of a deck of cards. Poultry and fish should be mainstays with pork and beef also fine if they are good quality. Eggs are fine, but try to eat eggs with vegetables as you want to reduce your acid and eggs are acidic. Vegetables will counteract that.