How do you remove fingernail polish from a carpet?
Spray hair spray on it once it is dry and scrub it with a small towel.
If your carpet is non-synthetic -- wool, for example -- it won't be affected by nail polish remover. If you carpet is synthetic -- very likely -- nail polish remover will likely dissolve the fibers where it comes into contact with the nap. This is not a "spot" that can be removed. Rather, it is permanent damage.
The best way would be to take it to an expert, in this case a dry cleaner. If you don't want to do that, you could try using fingernail polish remover, but you should try it in a tiny, inconspicuous area first to see if it has any adverse effect on either the material or dye used in the comforter (if it's made of synthetics, there's at least a reasonable chance fingernail polish remover will…