CANINE digestive enzymes are probably needed. Just a suggestion: do some reading online about it and then go with the one you think best. I am doing this myself right now. I did not know about this until I watched a Utube video by Dr. Karen Becker. Very important for all of our sweet babies because they are domesticated.
Instant mashed potatoes can also help some dogs with diarrhea. I have used them and the pumpkin puree and they worked.
I'm also reading "The Whole Pet Diet" by Andi Brown and so far am liking it very much. There is much information and knowledge in it and I'm very glad I bought it.
Wishing you and your darling Yorkie good health.