If he was just neutered, that will definitely throw him off. I hate to tell you this, but it can take up to a year to fully potty train a yorkie. Please do not take him back just for potty problems.
He just needs some patience.
yorkie_mama was describing what's called a "belly band". A number of YT members sell them. It fastens around the middle, and you put a panty liner inside, I believe. For many dogs, the sensation of having a wet belly is unpleasant enough that they will hold it when they are wearing one. On the other hand, some dogs may pee anyway.
I would definitely keep at the training before resorting to belly bands.