You need to wash it in Retayne in hot water. A lot of quilt shops carry Retayne now. You can also order it online from places such as Amazon, Dharma Trading, and ProChem. Just remember that Retayne *sets* dye. That's why you want to use it on a fabric. Never use it on a finished quilt, as it can permanently set a bleed. (Synthrapol can be used on a quilt to prevent bleeds from setting, and even to remove bleeds that have not been permanently set.)
A few fabrics need two treatments with Retayne. Anything that bleeds after that should be discarded or used for something other than a quilt.