Spray the mold down with a commercial mold and mildew remover. Make sure you are in a well-ventilated area to avoid inhaling the chemicals in the remover. Coat moldy areas of timber thoroughly. Read manufacturer's instructions for any special considerations for the brand that you purchase.
Scrub any areas, using a scrub brush, on the timber where the mold is visibly growing. The scrub brush will help to remove thick areas of mold.
Pressure wash the area to remove the commercial mold remover and to clean off any remaining mold.
Dry the timber at least 24 hours in a well-ventilated area. Do not use timber until it has dried completely.