Soak the item in milk for 30 minutes and then rinse it with warm soapy water. Apply lemon juice on the stain and let it sit out in the sun until it dried. Then wash as usual.
The following tips are for stubborn mildew stains on fabric. Make the mixture of 1 teaspoon of ammonia and 1 teaspoon of hydrogen peroxide for 1 glass of water. Cover stubborn mildew stains on fabric with this mixture and let it sit out for 10 minutes. Afterwards wash the item with hot water.