Remove and replace front seat belt

My daughter has a 2010 3dr 1.3 Ka Zetec.

Recently the front passenger side seatbelt has been jamming when you try to put it on. If you feed it out slowly you can eventually get it out. Teenagers and patience dont go together unfortunarely.

Got a price from a breakers for a replacement belt

Problem was removing the trim which is one large piece that covers whole of the rear internal quarter. 

Had to remove back seats, rear seatbelt anchor bolt which broke!!! PIA.

Anyway trim mostly off but at the bottom where the reel is at the anchor for the lap part. There is like a plastic part at the end of the belt that attaches to a steel wire then through trim into the pretensioner.

How does it detach to get through the small hole in the trim?

Any ideas or guidance appreciated.

Thanks