How do you get mildew out of clothes?

My daughter left a pair of her cotton shorts folded up wet and forgot about them. When she went to wash them, they have a mildew stain on the front pocket. Will baking soda get the stain out as well as the odor? She washed with only detergent and it did nothing. How do you apply the baking soda. I'm her dad, and I only know laundry detergent.