Put the Apple Watch on its charger and keep it there
On the Apple Watch, open Settings
Tap General
Tap Reset
Tap Erase All Content and Settings
Enter the passcode if prompted
If asked, choose to keep or remove your cellular plan
Confirm the erase
Wait for the Apple Watch to finish resetting
If Activation Lock appears, enter the Apple ID and password used on the watch
If you do not know the Apple ID password, use Apple’s account recovery or remove the watch from iCloud at iCloud.com/find
If the watch is managed by a previous owner, ask them to remove it from their Apple ID in Find My
If the watch is not accessible, use iCloud.com/find to erase it remotely if it is online
After erasing, set up the Apple Watch again as new or pair it with a new iPhone