Originally Posted by Russ Roth

You don't really need a tool to center a dual pivot brakes, tighten down the nut that holds it to the frame so its snug, don't over tighten. Grab the pad of the side that's rubbing and pull it away from the rim. That's it. The little screw being pointed to is something that virtually never needs to be touched. I've spent way more time adjusting that screw from someone else playing with it then I ever did actually using it.
However the pivot bolt just to the left of that screw is clearly loose and unadjusted. You'll need to tighten that up which I find easier to do without the cable installed in the caliper. You'll need to loosen the nut slightly, and start tightening the bolt. As you tighten squeeze the pads to the rim and make sure they snap back open, at the point they don't back off 1/4-1/2 a turn and tighten up the nut. After tightening the nut double check the pads snap back open, sometimes tightening that up tightens the pivots and you may have to back the bolt off a touch more. Reinstall the cable and center. With old school single pivots you had to use tools but with duals they just pull to the side you want and you can easily futz with them.