Rear seat belt replacement

I have a 2009 GEM E6. A few of the seat belts are not rewinding and need to be replaced. My husband was able to replace the drivers seat belt but has run into an issue with the rear seat. He is able to get the bench cushion seat and back off but can’t figure out how to get behind the seat frame to replace the seat belt mechanism. Hopefully there is an easy solution we have not figured out. Thanks!