you should have the brackets to do the job, if not........get some!
then its easier to take the bumper off and do it. offer up the bracket to the back of the bumper iron, it'll be obvious how it sits and use the (captive) bolts to tighten it down, do something similar for the lamp end of the bracket. then do the same the other side!
if your any way logically minded it'll take about 20mins.