If you need to unpair your Watch and don’t have access to your iPhone or can’t remember your Apple Watch passcode, follow these steps:
Here’s what you’ll see as you go through the process this way:
Alternately, you can go to Settings → General → Reset to erase and unpair your Apple Watch if you know your passcode, but the option above is faster.
If you need to erase and unpair your Apple Watch without your iPhone, you can log on to icloud.com and remove your Apple Watch under Settings → My Devices.