Unscrew the back and push the wire back up into the controller.
Home Depot sells grommets u could use. Now if the wire is broken pretty sure u will have to buy the whole dry side. Unless ur good at soldering
Actually, thinking of it, there is a multi-pin connector at the end of that cable (if wired the same as non-QD). Don't think I could get a geometry on there.
I've used a heat activated tape before now works like shrink wrap but in a tape form... I know I'm in the UK but if can find it you may be able to purchase something similar... I'll have a look now.