First (Highly recommended), factory reset your watch. Then set it back up and update WearOS (Don't worry about updating anything else) via the play store (You can sideload it too).
Second, after setting up your watch, go to settings -> system -> about then tap on your build number until you have unlocked developer settings.
Third, go to your developer options and enable ADB debugging and debug over Wi-Fi.
Connect to your Wi-Fi and click on the Wi-Fi network you are connected to, it should show your IP address (Take note of your IP address) and MAC address.
Assuming you already have ADB setup on your machine type:
adb connect your.watch.ip.address:5555
If that shows, great! If not, make sure you have authorized your PC on your watch.
Moving on, you want to get the list of Verizon apps installed on your watch so type:
pm list packages | grep 'verizon'
Next you'll want to uninstall them (All 5 or 4 of them. I can't recall as I have already done this). so here is the command to do so.
pm uninstall -k --user 0 com.verizon.crapware.mesagesplus
After you have uninstalled the packages, reboot your watch, and you should be able to see the apps that you have installed in the app drawer, and you should be able to set Google Messages as your default! Also as an extra measure, just disable all of the Verizon apps. They'll still show in your system apps, but if you click on permissions, it'll say "App isn't installed".
I'm sorry if the format is crappy. Also, mods, if you feel that this doesn't belong here, feel free to delete this post.
If you are having troubles doing this, I can clarify and help you guys out if need be!