My Dog Has Been Asked To Be A Therapy Dog For A Day. How Can I Prepare?

Well, sort of.
An old aunty of mine is currently in a nursing home in Bristol (England). My family and I should be going to see her soon. We asked if we could bring our dog, Hooch, as she was always an animal lover and they say they very much welcome animals under one condition: that the owners let the dog meet all the other residents, because some have had dogs in the past, miss them, and rarely get a chance to see them/pet them, so it’s a lovely opportunity for them. Another relative of ours often takes her Greyhound over there so they’re definitely allowed. I have considered getting Hooch assesed to see if he’d be eligible to become as PAT dog, as he’s so great with people, but it’s one of those things you plan to get around to doing but never do.
I have no problem taking him round to see all the other residents of the home. It’d be great if we could cheer them up and Hooch would love the attention. It’s just I have never done anything like this before. My dog is well-trained around people, very obedient and loving, but is there anything specific I should be doing? I just don’t quite know what they’re expecting of us. He’s not a trained therapy dog and I’ve done nothing like this before, so it’s definitely an informal arrangement. Do I just take him round to each of the people one by one and just let them stroke him and talk to him? A lot of the people in this home are really ill – dementia, strokes, all sorts.
Just a little nervous and would be grateful for any tips or advice.