Loosen the 2 bolts holding the caliper to the frame. Don’t remove them, just loosen them a bit so the caliper assembly can wiggle a bit.
Squeeze the brake handle to engage the brake. This will act to center the caliper assembly relative to the rotor. Do NOT release the brake handle.
Now tighten the 2 caliper bolts (while still squeezing the brake lever). After the bolts are tightened sufficiently, you may release the brake lever.
The pads should now be centered relative to the rotor. You can adjust the pad spacing if necessary (wider or closer) by using an Allen wrench to on the pad assembly. Turn clockwise to close the gap, counter-clockwise to make the gap wider.
Good Luck!! - RangerDave