Preparing my Apple Watch Series 4 that I recently sold

What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else

https://support.apple.com/en-us/HT208855

Here's how to prepare it for selling.

1. Open the “Settings” app on the Apple Watch and go to “General.”
2. Scroll down and choose “Reset”
3. Tap on “Erase All Content and Settings”
4. Enter the passcode for the Apple Watch.
5. Scroll down and confirm you wish to reset the Apple Watch and erase all data from the device.
6. Call AT&T and cancel your Cellular plan.