If like my coach, there are hidden screws holding the valance to the walls. I used a sharp pointy thing (dental pick) to poke around till I found them.
As far as restringing them, I did it once and then decided to just replace the shades. I used a set from Home Depot Home Decorators that are cordless and buttonless. You just use a finger to push them up. No buttons to push first.
The biggest drawback to them is the cats learned how to push them up at night so they can see outside!
It cost me around $300+- to replace all the shades in our coach back 3 years ago.