Check the trailer manual or the awning manual. Someplace there is a warning about using any bleach on the awning.
At the Jayco rally a few years ago it was recommended that a dishwashing liquid such as Dawn be used. As suggested in another post, apply the Dawn and water solution, roll up the awning and go have a cup of coffee or other refreshment. Extend the awning, scrub with a soft brush and rinse.
My opinion is that it is better to live with a spot than to apply any bleach to the fabric.
2014 Eagle Premier 361REQS
2013 Ford F350 Crew w/ 6.7 diesel