Vanish oxi action fabric stain remover is really good for mildew stains.Follow the instructions for the soak solution in a bowl and if the linings are attached to the curtains try and just soak the damaged part in the bowl and leave the rest of the curtain to rest on the draining board. Leave for about 20 minutes ,depending on how bad the stains are you may need longer. Rinse off the solution and wash the whole curtain as normal. You could try soaking the blind in the bath but that depends on the size.Then rinse it under the shower.