Sorry to say: I think the sweater needs to be thrown out.

You can try Carbona Color Run Remover.

You can also google remove color dye stain from clothes. There are many other fixes mentioned.

I suggest the Carbona Color Run Remover, too. You have nothing to lose, at this point. Perhaps a dry-cleaners can fix it, but since it happened in the wash, they can tell you if saving it is possible. The Carbona is cheaper. :-)

You might also be able to dye it a darker color if it is a favorite.

Could it be that you used liquid fabric softener?

If not that and another cool wash doesn't remove the staining, I would toss it. Out of sight/ out of mind.

If the Carbona doesn’t work, dry it flat and then try a combo of 1/3 blue Dawn and 2/3 hydrogen peroxide. Spray it on until saturated and wash again. Might work. Sorry!