How do cures for diseases come about?
These days? Astronomical amounts of research and testing.
200 years ago? Beat the patients and feed them random things. Try to remember what you did when they didnt die and see if it work on the next person.
When the US government says it’s okay to cure a disease. Same note, only if they make a lot of money off of the cure
Someone comes down with a sickness. Medical doctors and scientists take samples of what might be causing the sickness.
The medical doctors take known cures for similar sicknesses to see if any of those have an effect on the sickness at hand.
The scientists take their samples and apply a larger variety of chemicals/medications to more definitively see what may have an effect on the sickness.
Anything that works gets tested on a larger number of individuals before the authorities above will clear way for the solution to be published and advertised as the cure.