Often the best medication and treatment for fin issues...Is fresh like temp dechlorinated water from water changes, tannins, good nutrition and patience......
First you have to find the cause of the damage and remove that before healing can begin.
Fin re-growth can vary based on-age, genetics, fin damage cause, amount, severity of rot, overall health, how and timeliness of treatment and nutrition.
Often with some damage the fins will never return to their full glory, sometimes the new growth will look different and even a different color.
It can take weeks to months for the fin to re-grow-usually you will see white or clear fin edges as the first sign of new growth.
Good nutrition is a big factor in overall health, fin healing and re-growth
Good quality varied diet fed in small frequent meals and if you have access to mosquito larva offer several rinsed for one meal a day to boost protein intake to promote healing.