Read about 'What to do before you sell, give away, or trade in your Apple Watch, or buy one from someone else' - "Use these steps to remove your personal information from a device, even if you don't have it anymore. Or make sure that the watch that you're about to buy from someone else is ready for you to use." Click here --> https://support.apple.com/HT208855
Click on this link to read "About Activation Lock on your Apple Watch" --> https://support.apple.com/HT205009
For an individual to remove an activation lock absolutely requires the information for the account that applied the lock. Click on this link to learn 'How to remove Activation Lock' --> https://support.apple.com/HT201441
If you do not know the required information and you are not the original owner, get the owner of the account to remove the lock or return the device for a refund or recycle the device. The device is otherwise useless to you. If the owner is unknown and has not provided contact information as a message showing in the login screen, there is no way to contact the owner unless the person who gave you the device knows them.