To unpair an Apple Watch without the paired iPhone, you have a few options depending on your situation:

1. Erase Directly on the Apple Watch

• On your Apple Watch, go to Settings > General > Reset > Erase All Content and Settings.
• Enter your passcode if prompted.
• For cellular models, choose whether to keep or remove your cellular plan.
• This will erase the watch and unpair it from the iPhone, but the Activation Lock may still remain if not removed from iCloud

2. Use iCloud to Remove Activation Lock and Unpair

• On a computer or another device, go to iCloud.com and sign in with your Apple ID.
• Open Find iPhone and select All Devices at the top.
• Choose your Apple Watch from the list.
• Select Erase Apple Watch to wipe it remotely.
• After erasing, select Remove from Account to disable Activation Lock and fully unpair the watch.
• This method requires the Apple Watch to be online and you to have your Apple ID credentials

Additional Notes

• If you don’t know your Apple ID password or don’t have access to your trusted devices for two-factor authentication, unpairing and removing Activation Lock can be difficult.
• If you have forgotten your Apple Watch passcode, erasing via iCloud or resetting on the watch itself are your main options.
• After unpairing, the watch will be reset to factory settings and ready to pair with a new iPhone.

In summary, the most straightforward way to unpair without the iPhone is to erase the watch directly via its settings, then remove it from your Apple ID using iCloud to disable Activation Lock