I think when you begin to ride a horse, its the horse doing the riding.
I remember when I was at school we had a choice of things to do on Thursday and I chose horse riding. One day I was put on a horse that was known to be a bit aggressive. When the horse took off into a gallop I knew it was going to jump a fence ahead of me so I jumped off the horse. The horse jumped over the fence and I was lucky to not break my leg or something.
My point is get a good trainer and remember horses are powerful beasts.
Actually anyone who watched Game of Thrones will remember Bran who was paralyzed from the waist down. Another character Tyrion had something designed that allowed Bran to ride a horse.
A lot of places in New Zealand have Riding For The Disabled. Your country could possibly have the same thing. Google - Riding For The Disabled or talk to your caregiver or teacher or support person about this.