Rocky was "certified" by a local group and did visits for a few years at a long term care facility.
I'd start by seeing if there is a local group in your area that helps test/find placements for people just because that's easier (to me anyway). I liked that they had contacts in facilities and mentored new members (so first few visits I went with someone else and their dog, then they came to my visit visit with Rocky then I was on my own). Because I was in a hospital with their OWN volunteer program, I had a day or half day of training to get done there and used their volunteer log-in system and stuff.
The group I worked with tested via the TDI test found here: Therapy Dogs International
After passing we went to some info sessions and were placed in a facility (I didn't really care where, as long as it was closer to my place). Locally there are classes to prep for the test. Rocky really had the temperment for the job (which is why I did it) so we found out about the test less than a week before we went to take it :P He wasn't perfect, he doesn't have a gentle mouth (not that they are supposed to be fed at all during visits but some patients really really really wanted to give him stuff - it was hard).
They have rules. If I remember they didn't want dogs eating RAW (or not within 48 hours of the visit - but this will greatly depend on the type of facility you are going to). They also had some issues with washing the dog monthly but I honestly didn't do that.
I'd talk to the breeder if this interests you. Ideally find a breeder that has some puppies (or their own dogs) that have done some of this as well. They'll potentially point a specific puppy or two that would be a better potential fit.
Is St-John's ambulance a thing in the US? If so they have program for therapy dogs.
Surprisingly Rocky was FINISHED after an hour. he loves attention but short term. Plus as a big dog he can't just snooze on the bed with the patient. He'd have to sit on a chair.
I think Penny wuld have loved it too had we ever gotten the face licking and jumping under control :P I joked that she loved too much.