Ours have a clip in the middle to hold it in place while you install or remove two screws going straight up. You might have to kind of stand on your head and look up inside the valance.
We bought a CD and kit from
RV Shade and Blind Repair Forget what it cost but the parts are helpful as was the instruction CD. We have used string from the hardware store to restring a few of our blinds since then but still refer to the CD. Take you time and you will get the hang of it then anytime one of the shades has a problem you can fix it yourself.