Bettas are carnivorous fish, so they need a diet that is high in protein. They should be fed live food or frozen food, such as brine shrimp, daphnia, or bloodworms. Bettas can also eat pellets or flakes that are specifically designed for them.
If you do feed your betta tropical fish food, be sure to soak it in water first to make it easier to eat. You should also only feed your betta a small amount of food at a time, and you should avoid overfeeding them.