Household Chlorine Bleach is the normal to kill mildew. Use a compression sprayer ot apply the bleach to the surface, mixing the bleach 2 parts water 1 part bleach. Test in a small, inconspicous area first to make sure that the bleach will not remove the color. This may be an ongoing maintainance issue. You may find your self doing this once or twice a year to keep it from coming back.