What's the name for the string attached to a zipper to help close or open a bag?
The image shows a string attached directly to the slider of the zipper and not to its pull tab, which is seemingly missing. The pull tab is a tirette; the string is used as a replacement for it in the image:
Or the string is "connected" to the pull tab by its nature:
If the string was attached to the pull tab per se, then it's like an extension:
Rallonge à/de tirette.
Metonymic use might simply be tirette; some may reference its material (...en corde, en tissu).
In the end the tirette will go a long way...