The reason hash browns don't end up crispy is the amount of moisture in them. You need to press them in a clean kitchen towel or between paper towels to get as much of the moisture out as possible. If you have time, allow them to air dry for a few minutes which can also help them get crispy. You will also need to add some oil to the potatoes to make them crispy. I do this by adding olive oil to the shredded potatoes before putting them in the air fryer, but you can also spray them with additional oil at the halfway point, if you don't think they're getting crispy enough.