Hi marguerite29,
Thanks for posting in Apple Support Communities! In order to set up cellular service on your Apple Watch, follow these steps:
- "On your iPhone, open the Apple Watch app.
- Tap the My Watch tab, then tap Cellular.
- Tap Set Up Cellular.
- Follow the instructions for your carrier. You might need to contact your carrier for help."
Find more details and information on using cellular on your Apple Watch here: Set up cellular on Apple Watch.
If you've already followed those steps to get it set up and you're still unable to use the network, make sure that your iPhone and Apple Watch are both running the latest software versions.
You also may need to update your carrier settings: Manually update your carrier settings on your iPhone or iPad.
Should you continue to experience this issue after performing the above steps, contact Apple Support for further assistance.
Cheers!