@pdhspondi2 I did a search and found this website where you can search for certified horse equine assisted therapy places. I selected Missouri on the left side, and scrolled down to see lists of centers. There seem to be more listed below than on the map if you keep scrolling.

PATH International
https://pathintl.org/find-a-program/
We also have this discussion on Connect.

Just Want to Talk- "Equine therapy is horses helping people how do horses help?"
https://connect.mayoclinic.org/discussion/equine-therapy-is-horses-helping-people-how-do-horses-help/
I know just sitting on a walking horse with good posture helps build core strength because you have to counter the hip movements of the horse with your back muscles so it is like you are waking without your feet on the ground. If you are not familiar with horses and riding, someone should control and lead the horse so you can work on balance and sitting up tall with good posture. Only you know your capabilities and they do this with disabled individuals with spotters next to the horse in case bad balance would cause someone to start to fall. You need a calm horse too. There is probably a lot more to it than that with a trained therapist and a lot of riding a horse is by feel and awareness.

Sometimes my pelvis shifts out of alignment, and recently it happened while I was trail riding (walking) and it sent a pain from my groin down my leg. I had to get off my horse and do an exercise to realign my pelvis that my physical therapist taught me, and then I could get back on my horse and finish the ride. That never happened before, but if you have similar issues, riding a horse may not be good. You may be able to use a big therapy ball and sit on it simulating a walking motion, but please ask your medical professionals what is right for you and safe to do.