I just scrub it with a regular housewash mold and mildew remover. I let it hang down from the edge of the camper with the top up. The underside is harder to do, you have to have someone hold the awning away from the camper. I use a soft bristled broom to scrub it.
LOL, I just did this a few weeks ago. I just flipped the awning over the roof and use a bleach and water solution and a mop. Didn't have mildew but lots of dirt and leaf impressions from rolling it up when wet. No before photos but here's the after.
I use high quality cleaners for cleaning then spray again the protective coat so my awning is thoroughly protected, the awning stays cleaner for a long time and does not change color, the texture of the fabric