Not sure what year you have but, there should be the bolts that hold it at the top of the bumper (near trunk lid), the front corner bolts (by wheel) and maybe some up under the rear lip (?). If you have marker lights, unplug them.

I just had to loosen the front bolts and push the bumper foward to close up the gap, then tighten the bolts to hold it there.

If your white plastic clips are broken, try an online dealer or your local dealer.