On mine, I drew a straight line down the length of the bar with a sharpie. This gave me a line to follow when I put the hard part of the velcro on it.
Add the soft part of the velcro to the cloth leader. I centered this so I put it on in two pieces, each going from the center to the edge.
Once you have the velcro in place, you simply put the leader on the rod by aligning the center and going out to the edges.
I hope this helps you. It goes together pretty easily.