mustard stain?

Left my room spotless to go on a trip and came back to it destroyed by my brother. I'm talking dishes everywhere, clothes everywhere, pillows and blankets everywhere, pizza boxes on my bed, a fork with whip cream on it stuck to my carpet, and a dried mustard stain on my white comforter. Yes, I was pissed. Yes, I went off. That being said, does anyone know how to get a mustard stain out of a white comforter? 👌🏽😑