The rubberline is pulled through the QR like shown on the picture. Pull both ends through the chickenstick (less wider end of the stick to the QR) and hold them tight. Put the small black ball over the line, make a knot above it and let the rubberband pull the ball into the stick again. If some line looks out of the stick, simply cut it. Here you go! Get the 1.0 chickenstick here:

If you own the Rotor 1.1 Quickrelease that comes with all Sensor2, Sensor2+ and Sensor Pro Bars, it is slightly different and much easier. There's a different chickenstick 1.1 for that one:

With that one it's much easier to replace it. Simply pull the white rubber line through the hole in the QR and let the metal part get locked in it. Pull the rubber line through the chickenstick, stretch it, make a figure eight knot at the black mark and let it slip in the chickenstick again. If tension is OK, simply cut all unnecessary parts of the rubber line. Easy like that!