I would seriously get a trainer or someone to help you with this. There is more to it than just getting over the jump and it starts with a solid foundation in flatwork which helps make jumping easier. Good luck!
Start with poles and get them comfortable with that. Then start slowly and only with one! Have patience
I would start with a pole in the ground, do a corridor and let him pass free running through... then slowly increasing the height... when he knows what are you asking for, you can do it riding him.