prius c loose front fender

That looks like the front bumper. If it's the bumper it clips in and if it won't clip in then the clips probably broke and you need to replace them or bring it to get fixed. If that's the fender then yo need to bring it to Toyota or a body shop to fix. Try pushing in on it around the seems where it meets along the bumper and see if it snaps back in

 

I would take it to a body shop.

 

I'll resuscitate this thread, since i have a similar issue. I've been struggling to identify the part number for this clip, which is clearly missing. I found this diagram for the front bumper on lakelandtoyota, but it's not very clear what's what.

Would appreciate the help tracking down the part! Thanks!

 

I believe the part your looking for is #6, in your diagram. Do a very close inspection of the edges of part #1. If the lock points are not intact, ripped out; replacing part #6 won't do you any good.
I removed part #1 on my old 2012 Prius C, to push out a dent - those lock-tabs are pretty brittle. Try just pushing it back in, to see if it'll locks back into place.

Good Luck...