Removing Mildew Stains
Apply detergent to the stain and launder. Mildew has weakened the fabric so we need to be gentle with the item. Sometimes when we get the stain out of a badly mildewed item, we have holes where the mildew was.
If bleaching is needed, soak for 10 to 15 minutes in a solution of 1/4 cup chlorine bleach in 3/4 cup water if it is safe for the fabric. You could bleach with an oxygen-type bleach. Rinse and launder.