Hi.
Cleaning out the whole tank could have killed a significant portion of the beneficial bacteria.
Check out my signature link for an important article which helps about keeping a happy fish tank. As soon as you have a few minutes.
You need to check the water quality.
Do you know the
Ammonia
NitrIte
Nitrate
pH
TDS
KH / Calcium/Alkalinity
GH /General Hardness
Unsafe levels of ammonia, nitrite and nitrate will cause illness and or /death.
First thing is perfect water quality giving the fish a chance to heal.
But medication may be necessary.
Get the water changed to perfect water parameters.
Once you know the water parameters that will help a lot. A liquid test kit is the most accurate way to know what is going on.
In the mean time do a 1/3 pwc /partial water change, and then refill with treated / dechlorinated water with the temperature matched to the fish tank water.
then do another one 1/3 pwc. if the fish seems to perk up a little that is great.
Do another 50% pwc after a few more hours and then one more 50% pwc the next day.
This will gradually make changes to the water quality of the fish gently, helping to make the water better and better but fairly quickly since he needs help asap. It is done this way to make it easier for the fish to handle changes.
Or you can use a liquid test kit to know where the water quality stands and what is in fact safe water for him.
Additionally if after getting the water safe. And the fish seems better but not yet healed from the swim bladder condition you can try Epsom salt therapy.
https://www.aquariumadvice.com/forums/f17/using-epsom-salt-in-fish-therapy-374191.html#post3548383
If the fish has not become more active or any better after the water changes then it will need medication.
You might try Kanaplex which is kanamycin. It will be absorbed through the body of the fish so he doesn't have to eat it to get treatment.