i just watched this video, and found it very easy to follow. Thought I would share it. It was probably the most simple way I have ever seen it explained. I will also include the link for dosing. If anyone needs it. Oh and this doesn’t just apply to Betta fish. It can work well for most fish. (If it is a scaleless fish, I wouldn’t use salt at all).
http://bettasplendid.weebly.com/salt-baths.html
http://bettasplendid.weebly.com/salt-baths.html