Watch face is loose

I would get it fixed before it comes apart. I'm sure the water resistance is compromised.

For repair & service:

Apple Watch Service & Repair - Apple Support

This is typically caused by a swollen battery. You haven't provided any details regarding which Apple Watch model you have, so I've no idea if AppleCare is an option or not.

Recommend you use the link provided by javaliga if you're inclined to repair the watch rather than replace it.