This is a strappy dress. One strap is twisted and I can't figure out how to untwist it so that the strap folds over onto itself parallel and flat. The dress is a very soft and can pass through both the strap loop and the arm loop. There is an inside surface and an outside surface.

Cutting the strap is not an option.

A female friend's nighty is in a twist, and I've been trusted to untangle it because I'm "good at maths" but I can't solve it.