The brakes should have a knurled knob where the cable attaches. Back the knob out a little to adjust the distance from the pad to the rim.

As dbakl wrote, the bolt usually has flats just in front of where it goes through the fork (or behind the brake bridge on the rear brake). My Campy brakes have a 13mm flat section there. I use a Park offset brake wrench OBW-1 to grab the flats and center the brakes. That rotates the entire assembly.

BTW, I don't think Park makes the OBW-1 now. It was perfect for the 80's Campy style sidepull brakes, but I guess they redesigned the tool for newer brake styles. A thin cone wrench will work, it's just not as convenient.