After using products to help it you could try to put it in a tail bag if it's long enough. It promotes hair growth and can help protect the tail.😊
MTG is my absolute go to product! It will do you wonders it is also great with fungus, rain rot, and is the best for rubs
Stinky stuff is great. You can get it online. My pony has sweetich and rubs out his mane and tail. Stinky stuff stops the midges from wanting to bite, heals sore areas and incourages hair growth
Rub some coconut oil on it :) Just don't put the oil on the mornings if your horse is going out on a sunny day.