To lower nitrate, suction the gravel with a turkey baster or a vacuum. Also, nitrate is DEADLY so get it out of there ASAP. I lost my favorite to nitrate poisoning...
Also, nitrate quickly converts to ammonia. I use a sponge filter to help eliminate it. If you don't have one on hand, I would reccomend moving your fish to another tank temporarily and give your main tank a good cleaning, maybe a 50 percent.