When a fish is moribund, close to death, there is rarely anything that can be done for it. Damage control is most important, trying to ensure whatever is wrong with it doesn’t spread to other animals. Sometimes, if it is a water quality issue, moving the fish to a new tank can save it, but if it is a disease, medications aren’t going to work fast enough.
Below my name here is a link to a file that outlines what unfortunately is helpful for us to know about your tank in order to figure out what is going on.
Jay