Decided to tackle the broken string on the four string shade over the sofa.
I used 1.2mm String, Cord and Parts for RV Day Night Shade Repair.
as my vendor and bought everything I thought I might need. After doing it I can save you some money as I was able to string it without the needle and wire.
The hardest part was getting the correct color string. There are four "off whitish" colors of string. I lucked out getting one only "slightly wrong" trying to hold the string up to the monitor. Repaired you can't tell it is slightly lighter than the original.
I used the old string as a "fish" to pull the new string through the bends in the shade. I found that scotch tape and looping the string as shown allowed it to be carefully drawn through the shade and only had a bit of trouble with one run out of the four. If the string is hard to pull - MAKE SURE the blinds have not slipped out of alignment. The edges must be even for the holes to line up in the bars.