To remove mold and mildew from your canvas tent, or awning, first vacuum or brush soilded areas to remove any excess dirt. Wash the affected area with a solution of 1/2 cup Lysol to a gallon of hot water. Rinse with a solution of 1 cup lemon juice and 1 cup salt to a gallon of hot water. Allow the canvas to air dry in the sun.
You can also try applying a cleaner such as IOSSO Tent & Camping Gear Cleaner. This cleaner is made to remove tough dirt and mildew stains. Afterwards, you may want to treat the canvas with a water-repellent compound such as Canvak.