Those pesky day/night shades can be repaired when the strings break.
We successfully repaired 3 day/night shades in our Laredo. There are a number of videos to look at but this one is the best.
Here's a good PDF with drawings for the various types of blinds.
www.discoveryowners.com/DayNightCompile.pdf
We bought the right color string from fixmyblinds.com They have everything, all sizes of string, springs, the small gripper knobs at the bottom etc. They delivered within days.
Remember to keep both day and night sections facing front. I think we discovered most things to do wrong and had to take back down and redo. Thankfully we discovered we didn't have to take off the valances.
If your strings broke because they were too tight make sure to give yourself more string next time.