If the turn signal was indeed "dangling," its mounting tabs are broken and it needs to be replaced.
I tackled this little project last night and it all went well. It seems the 2018 turn signal design doesn't screw into place the way the illustration in your earlier model pdf shows. It snaps/clips into place and was intact. But when it popped off, the clip held on so strongly that it tore out a chunk of plastic from the mirror's skeleton onto which it was mounted -- about the size of a quarter.
Here are the steps I took to fix it:
- I found that quarter-sized chunk on my garage floor (under my nearby generator!!) and fit in back in place without crazy glue
- Snapped the turn signal to the broken chunk wedged back into skeleton
- Slid the top of the top mirror cover into place, then swung it down to engage the clips
- Worked the bottom mirror cover on and clipped it all around (one clip was sneaky near the pivot point for the mirror)
So, now that loose chunk is just being held in place by tension and I'll see how it goes. I really don't want to replace the whole mirror assembly.
All other claws/clips were intact on the covers so it went back together nicely and easily. And luckily,
no scuffs on the painted mirror cover despite bouncing onto the garage floor! What stinks is the car is only three weeks old and already "broken." I'll get over it.