How can I fix this watch?

I have an expensive watch I never wear. I was thinking about selling it, so I took it out and promptly dropped it. The link that surrounds the glass faceplate came loose and I can’t figure out how to get it back on properly. It came off so easily it seems like it must be an easy fix. I can’t see any loose screws or something that actually looks broken…is there a trick to this?

I took some pictures to try to better explain the problem.
Here is the watch with an arrow pointing to the piece that came off.

This is what it should look like from the side, with the broken piece pushed back into place.

But this is what it actually looks like, with the broken piece loose.

Is there an easy fix or should I take this guy to a repair shop?