The things that I know of that have helped, are the following:

Glutathione (IV)has been used for breathing problems successfully. More research is needed before using it as a Covid treatment.
My practitioner has long Covid (irregular heart beats) and she uses a nicotine patch with some success. (One of our members says it alleviated all her symptoms.) My practitioner also swears by Oregano oil with black seed oil to stop infections.
One of our members said arginine cleared up all her long Covid symptoms.

From what I have gathered those hospitalized for Covid or have long Covid can be low on one of the following: B12, iron or glutathione.