just underneath the metal fender between the headlamp and the fender flare is a black plastic bracket. there are tabs on both the bracket and the edge of the bumper cover. these hold each other together. but the corner of the bumper is ripped. there is a 10mm screw that holds the corner to the fender in this corner, this is what keeps the bumper from falling off. you're going to need a new bumper cover because you can no longer secure the cover.
you can try to pop the cover back on, but the corner will still be floating and any light tap or force can pop the cover back off.
The little tab where the bumper covers screws to the fender broke off. You could try and fix it by getting some high-strength epoxy or JB Weld or something and affix it back into place. It may not be perfect, but it's cheaper than a new cover.