I am NOT an Apple employee. I’m just a user like you.
In your original post you say you do not have WiFi.
The Apple Watch requires WiFi to update.
If you can enable your iPhone as a Hotspot, that might work, but I am unsure.
Share your internet connection from iPhone - Apple Support
Another approach might be if you can have your Mac use the iPhone Hotspot, and then have the Mac enable Internet sharing via System Settings.
You could get a MiFi device from your cellular provider and set up WiFi for the time you need it.
You could visit an Apple Store and ask them for aid and assistance.
You could visit a neighbor or family member that does have WiFi
As I am a user, just like you, I cannot change how the Apple Watch gets updated.