well first fast him for 2 days and then his feeding schedule should be 2-3 pellets a day. because his stomach is the size of one of his eyes. and it would also help if you soak the pellets for about 5 mins exactly because the water will make them expand in his stomach and will make him look bloated either way.
so fast him then only 2 pellets a day and first soak the pellets before giving them to him:) after that he will be one happy betta:). also if you dont want to you dont HAVE to soak them. IME i dont soak them but it will help if you do so that is your choice:)