The balances of these windows are not really designed to be serviceable but, fortunately, they are only $10-$25 (size dependent)Â replacement parts. The spring that pulls the cord has stretched or detached for whatever reason or the balance wasn't the right size to begin with.
There may also still be a chance that a simpler issue prevents the cord from retracting: it could have slipped from the pulley at the end of the balance or the pulling mechanism has become blocked with some dirts and you can clear that out and let the cord move freely. It may work if the spring itself is still OK.
Either way, you would need to remove the sash and have a look at the balances. You can then do both: write down the replacement part number for a new balance and at the same time take the balance out of the channel and review closely for any loose parts, dirt and spring detachment. If you cannot locate obvious and easily removable obstruction, you can then use the part number to order replacements. Otherwise, you may get lucky and free the cord.
Andersen has a guide for balance replacements - they have to go by proper spring tension for the pane weight and the cord length for it's height. Also, the balances differ for standard Low-E glass and for tempered glass, so be careful ordering replacements.