Channel balance replacement

I have a sash balance for double hung window marked on the channel is 26-4, check on your website, cannot find the picture match mine, could you help to identify the Part No. For me, also for the cord broken in side the sash balance channel, do you have video shows how to replace the broken cord? Or we cannot do it by ourself need special tool to load the spring then put cord on? Thank you very much for help!