Apple Watch Sell, give away, or lose Apple Watch
Before you sell or give away your Apple Watch, be sure to unpair it from your iPhone. This erases its contents, including payment cards, and removes Activation Lock (which prevents someone else from activating it). If you lose your Apple Watch, you can mark it as missing. This unpairs Apple Watch and erases it, but doesn’t remove Activation Lock.
Unpair Apple Watch and remove Activation Lock. Open the Apple Watch app on iPhone, tap My Watch, tap Apple Watch, then tap Unpair Apple Watch. Apple Watch is erased, removed from your iCloud account, and Activation Lock is removed.
Mark Apple Watch as Missing. Open the Apple Watch app on iPhone, tap My Watch, tap Apple Watch, then tap Mark as Missing.Your information and payment cards are safe and no one else can activate your Apple Watch.
Remove payment cards using a web browser. If your Apple Watch is lost or stolen, you can sign in to your account at iCloud.com and remove your cards. Go to Settings > My Devices, choose the device, then click Remove in the Apple Pay section of the device info. You can also call the issuers of your cards.
If your iPhone and Apple Watch are no longer connected, or if one of them isn’t functioning as expected, erase the contents of Apple Watch first, and then unpair it using the Apple Watch app on iPhone (if available).