Pella Double Hung window problems

One of the pins that my Pella window hangs from when tilted open for cleaning has broken - And the balance mechanism that the pin rests on has slack in the string and will no longer assist in raising the window. The other side (Good Pin pictured) is working fine and is able to do all the work of raising the window but I am concerned this will not last and would like to fix the broken side. Replacing the broken pin is obvious and simple, but the string from the balance mechanism disappears as it goes up into the window and I'm not sure how difficult or involved this repair will be. Can you assist?
Thanks.
Paul