Wanting To Fix Dent In Right Butt Cheek from a Steroid Shot That I Got when I Was Younger. How?

Hello dear!!
Thanks for the question and provided information as well. 
You are probably a good candidate for fat transfer, to improve your buttocks. Unfortunately, without pictures, it is very difficult to give you a proper answer. l recommend you to make an appointment with a board certified plastic surgeon to talk about your goals and anything you need to know.
Good luck :)

The only reliable safe, long-lasting filler used in the buttocks is your own fat. The amount of fat needed would depend on the depth of the defect and if you wanted more than the indentation to be augmented.