Very little you can do really once in this state I'm afraid. Expect the worst.
Sorry to be harsh but there's no point buttering it up and giving you false hope.
Ok, well it could be a number of things, first thing is ruling out dropsy (you can say bu bi if it is) horrible thing that! first i would get yourself some tank states and post them here, what size is the tank, is there any tank mates? how often is he laying on the bottom? does he come up for food? how does he react when you move close to the tank?
Hm, well feed him some deshelled boiled peas, im not a pro but i had the same issue and this sorted it, when he poos what does it look like?
Ok, well boil a pea and de shell it, feed that to him (and make sure the other fish dont rob it lol) and just take note of his poo, (if he is not poo'in this could be why he is bloated) thats what you want to hope anyway, otherwise it could well be the start of dropsy, I lost my betta to this in a bad way (took 2 months before death was horrible) so keep a close eye on the little guy!
Hm, well feed him some deshelled boiled peas, im not a pro but i had the same issue and this sorted it, when he poos what does it look like?
not noticed to be honest
....well sounds like something is not right but his bowls are moving, is he still bloated? what does the long stringy poo look like?