The fact that the fish is not eating makes me thing we are talking something digestive. But this also limits the potential types of treatments that can be used.
Some folks believe that Epsom salts will relieve constipation in fish, other do not. The Problem with using Epsom is that it makes the water harder fast. So using this with fish which naturally prefer softer water and lower pH can react poorly.
The only fish I have treated with Epsom was a swordtail. I was not sure if it was constipated or fry bound. I combined salt and Epsom and after a few weeks it was back to normal with one exception. It was a Fm fish and, after it recovered, it never gave birth again. If I were to suggest this sort of thing, I am not sure for your fish if a lower level treatment in the H tank or a stronger treatment as a dip in a bath would be the best alternative if doing this.
Next, I cannot say why your fish is plugged up which means I cannot say what might be a good treatment. There is always a chance it recovers on its own, especially if it is just garden variety constipation from over eating or eating the wrong thing. But that is a somewhat longshot.
If you are putting it into the 10 gal., if you have some fakes plants, add a few. Being able to hide lets the fish feel safe, which means less stress. Hopefully, you will see any poop or expelled worms if there is any of either.
Adult fish in good shape can go some time without eating. Years back I purchased a lot of used tanks and equipment from a cichlid breeder whose back surgery forced him out of the hobby. He needed to sell everything, especially the fish. They did not move out fast. He had stopped feeding the tanks. I visited several times over about 5 weeks to negotiate and then to pickup a pair of 6 foot tanks and all the equipment with them. His fish were always there and mostly still alive.
In your case, if the fish does not get better and resume eating, it will weaken and die. So, you may have to use the "take your best shot" treatment methodology.