Yeah, there is a plastic rivet there( with I believe a thin plate of metal inbwtween). Just go to the local hardware store & get yourself some 10mm bolts, a few nuts & the biggest washers they have that will fit on the bolt( it isnt hard to figure out once you realize ho weasy it is to fix). As for the force needed, yeah it will be hard to pull them together with your hands.
BUT remember to throughly check your bumper for anything else that may have came loose. I highly doubt anything else did. They make those like that for a reason believe it or not. better the rivets break, than ripping a hole on each side of your bumper.
Replace the rivets with the bolt & watch how you drive next time
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Oh yeah...take off as much as the fender liner as you can..it makes it soo much easier.
I have fixed this type of damage more times than I can count or care to think. It is very common.