If you cooked them before freezing, you can simply microwave the frozen patties for 30 seconds at a time until heated through. You could also bake them in the oven straight from frozen. Bake at 350°F for 15-20 minutes, until heated through, flipping them halfway through. Or they can be cooked in a skillet on the stove over medium heat for 12-14 minutes, flipping every few minutes.