unpair apple watch without iphone

On a computer, go to iCloud.com and sign in with your Apple ID.

Go to Find Iphone.

Select All Devices, then click your Apple Watch.

Click Erase Apple Watch.

Select Next until the device is erased.

Click the remove button next to your Apple Watch.

This removes the Activation Lock as well.

go to settings -> general -> reset

it will erase all data and reset watch to factory defaults