1. Try using high-temperature water. Usually heat transfer will remove some of it, but it will be more unsightly.
2. The best way is to ask someone to use dark paper (heat transfer) to print a pattern on the original place, or print a heat transfer with American foam. Complete coverage, no removal to speak of.
3. If the clothes are of solid color, you can try washing them with a stain cleaner. If there are many colors, do not wash them.