Apparently the idea of ulcers being caused by steroids has been proven untrue.
I've been on steroids many years without any issues.
I would expect treatment to be the same as for any ulcer. Here are some foods to eat and some to avoid.
https://health.usnews.com/conditions/digestive-disease/peptic-ulcer/articles/stomach-ulcer-diet-foods-to-eat-and-avoidGood luck.