Hey mate, Press the function button on the watch and go to Settings > Sounds > Volume to modify the volume settings.
Two troubleshooting tips if this does not help. (1) The speaker hole may be blocked by a foreign object so, clean it. (2) Adjust the volume on your phone to check if that influences the watch volume.
If the above steps does not help, press the button go to Settings > System > Reset. Then, check again to see if the issue is resolved.
Failing all of that, contact CMF Support 🙂