Never be scared to underfeed him because they can live up to 30 days without feed. It is better to feed it 3-4 betta pellets(tiny size) per day, but not 4 pellets at once because they can consume it. Try to break it into two times per day(Morning 2 pellets and before you sleep 2 pellets).
Feed him once or twice a day, making sure that you are only giving him an amount that he can eat in five minutes. If there is excess food in the tank after five minutes of him eating, you need to cut down on the amount you're giving him - this will prevent overfeeding.
Well i had a betta and i fed it twice a day! I also fed it just a little picch probably about 5 or 6 pelets in the morning then about 3 to 4 pelets before you go to bed! I did that to mine and they lived for 3 years but then they died! :-( or if they are big ones then do lese then i told u!
you should feed him three pellets once a day or half of that twice a day.
and skip a day once a week to prevent constipation!
you should soak the pellets in warm water for a minute before giving it to him or it could blow up inside him! :[
good luck!