Before you microwave a sweet potato, make sure you scrub it and clean it using running water. Then use a fork to pierce the skin of the sweet potato up to 6 times. Place it on a microwave-safe plate, turn on the machine, and wait for 5 to 10 minutes. After rotating the potato, microwave for an additional 2 minutes. Keep piercing it until you can feel the fork going through without resistance. Cook for additional intervals of one minute if the potato remains hard.