You want the potatoes very thick, so add milk in tablespoon increments. (edibleperspective.com)
Add reserved all - purpose flour in 2 tablespoon increments until the dough is smooth and soft *, pulling away from the side of the bowl when stirred. (e2bakesbrooklyn.com)
I'd say if you gave them a second go to mix everything but the oats together, and then add a 1/4 cup of the rolled oats to the mix at a time, possibly adding it in tablespoon increments after the first 1/4 cup, until the mixture thickens but is still gooey enough to hold together. (faring-well.com)