Check Amazon for boat canvas cleaners and protectors. I like the 303 products.

https://www.amazon.com/303-Tonneau-Cover-Convertible-Cleaner/dp/B0185PU376/ref=sr_1_9?crid=17DJNXDKR9SXB&dchild=1&keywords=boat+canvas+cleaner+and+protectant+303&qid=1596602466&sprefix=boat+canvas+cleaner%2Caps%2C375&sr=8-9