Skip the microwave or the skillet. Once you reheat hash browns this way, you will never want to try any other method ever again.
If you do thaw them, you can also pat them dry with a towel to help pull out any excess moisture and ensure you get a crisp ...
After 10 minutes in the waffle iron, the hash browns only had a little bit of color and they hadn't really crisped up at all. I didn't like the soft texture, and with the addition of egg and flour ...