Frozen hash browns are blanched and flash frozen in huge freezers.
The frozen hash browns are not really precooked so you should cook them by putting them in the oven or in a skillet.
You can eat the frozen hash browns without cooking them once they thaw out because raw potatoes are safe to eat and you don't have to cook frozen hash browns or raw potatoes before cooking them.
However cooking the frozen hash browns will make them much more enjoyable.
Cooking frozen hash browns in the skillet takes around 2 to 4 minutes and after a minute or so flip the hash brown over.
For cooking the frozen hash browns in the oven it takes around 10 to 20 minutes depending on how well done you want your frozen hash browns to be.