To make your canvas tent white again, start by washing it thoroughly. Mix a mild detergent with warm water, then scrub the tent gently using a soft-bristle brush. Rinse the tent thoroughly to remove all soap residue. Next, apply a bleach solution directly to any stubborn stains or discoloration. Use a mixture of one part bleach to four parts water, and scrub the affected areas carefully. Rinse the tent once again to remove any remaining bleach. Allow the tent to dry completely in the sun. If any yellowing or discoloration remains, you can try using a fabric whitener or canvas brightener specifically designed for outdoor fabrics. Follow the instructions on the product packaging for best results. Regular maintenance and cleaning are essential to keep your canvas tent looking fresh and white.