I just made one up on my own
I'll try to explain, don't have a visual sorry:
I made the shape I wanted, a rectangle with one side more narrow than the other (or a long triangle with the pointy tip of the long side cut off. Turned and topstitched all , leaving the bottom (wide end) opened to place the loosely trifolded end of toweling, making sure the topper hole is folded in; topstitched it shut, then put a snap on it so it can fold over and stay attatched. Was that clear as mud?
You can also make the towel end as wide as the towel, and make the narrow end as narrow as you like or even bring it to a "strip" (as long as you can t/ts) and either use a buttons, snaps, or aplix.