Not sure what you mean by "popped it's string" but if the string didn't actually
cut itself apart, the blinds are easy to repair yourself.
At the bottom of the day/night shade on the metal ridge, take off the "end caps". Now gently push the day/night shade a few inches out of the metal ridge on the "good" side that the string is still on. Look at how it connects. Now push the day/night shade in the other direction to now expose the "bad" side and you can compare and see how the sting should be connected. Just make the "bad" side string look like the "good" side string.
I've done this to almost everyone of our blinds and we have a couple that I have had to repair twice over the last 7 years that we have owned our Montana.
My husband has tried to fix the day/night shades and he can't figure it out. Or he is playing dumb so I'll fix 'em. No matter what, you just need a little bit of patience and they repair up real nice.