Try to spend as much time with him so he gets to know you. Then do an “evaluation” ride to see how green he is then work from there. Also do lots of desensitizing so he gets used to things. I also recommend to take him to many different places so he gets used to being somewhere new.
Just be patient and start out slow. It also depends on how green he is. Like is he saddle broke? Can you ride him? Also make sure to desensitize young horses to different things sack him out etc, because green horses spook more than experienced horses. Overall be positive and encouraging. Don't get mad if they don't do what u want right away