Lost my Applewatch. Bought new series 7. How do I transfer my cellular service to the new watch?

Transfer your mobile data plan to a new Apple Watch

When you’re ready to start using a new Apple Watch, you can transfer cellular service from your old watch to your new one. Here’s how:

1. Remove the mobile data plan from your old Apple Watch. You can do this from the Apple Watch app or by erasing your old Apple Watch. 
2. Pair your new Apple Watch with your iPhone. During setup, tap “Set up Cellular” to add a mobile data plan.
3. Some network providers allow you to transfer your existing plan to your new Apple Watch directly from the Apple Watch app. 
4. If you don’t see an option to transfer your mobile data plan, contact your network provider for help.