You are automatically the GM of any game you create, though there is an in-game button you can use to rejoin as a player. You are automatically a player in any game that someone else creates to which you are invited, though the creator has the option to promote you to GM. You shouldn't need to change anything, that works and reads the same way for every user. Let me know if that didn't answer the question you were asking, or if there is a specific place where you are called a GM, post a screenshot of it and we can work it out.
