While you wait for answers, we may have found some information which could help you.
Click here for Repair Blind Blindshow can i reglue my honeycomb shades?
How to retension a Velux blackout blind GGL4?
I need to shorten draw strings ?
Refixing a velux blind?
Replacing cord for high Velux window?
How can I fix my velux blackout blind GPL 308 with broken cord?