When you have young fry that are having buoyancy issues....it can be from several things. Genetics, deformities, type/amount of food, water quality, poor nutrition, too cool dry air over the water to name the most common causes.
Sometimes it will resolve on its own-and it will either come back as they mature and sometimes it doesn't-and while a Betta with buoyancy problems can generally live a normal life albeit limited-it can be worrisome to the hobbyist. Personally, I cull fry that have any buoyancy issues that don't resolve on its own within a few days.
What kind of food are you feeding and how much/often, tank size, water level, substrate, filter, live plants, additives used, how much and how often are the water changes, water temp. Are you using anything over the top of the tank to retain heat/humidity if the tank isn't in a warm/high humidity room. When did the symptoms first start, is it all the fry (how many) has any got better on their own, have you tried any treatments.
what tail type are the parents and do they have any buoyancy issues-past or present-history of.....
Besides the buoyancy issues...any other signs/symptoms....