No strap on main awning. How do I know the length I need?

Okay. I called the number of the place from the link that you posted about Faulkner awnings. He said it needs a strap. It's so weird cause the booklet doesn't show a strap as one of the parts and neither does the schematic on the website, but he said I do need a strap. So, since I ordered it on Amazon rather than looking for one locally, I wait.

I was afraid to try and manually roll it up cause if I release the spring and the thing goes flying out of my hands and crashes up against the rig, it's bye bye awning.