How can I use my Apple Watch if it’s link to someone else account

Unfortunately, the Watch would need to be unpaired or be removed from Find My iPhone by the original owner. I recommend reaching out to the pawn shop to see if they have contact with the original owner. Otherwise, the Watch will remain Activation Locked and you won't be able to set it up.

For more info, I recommend looking over this article - Turn off Find My iPhone Activation Lock

Hi

You are describing Activation Lock, which prevents unauthorised use of Apple Watch if it is lost or stolen.

The previous owner should have removed the lock before selling their device.

To be able to pair the Apple Watch to your own iPhone, you would need the previous owner (who may not be the seller) to either enter their Apple ID and password on your iPhone or to turn the feature off via https://www.icloud.com/ (by signing in with their Apple ID > Find My iPhone > All Devices, then select the Apple Watch > Erase Apple Watch > Next until erased > click X next to the watch).

If you cannot arrange for the previous owner to do this, then you should, if possible, return the Apple Watch for a refund.

I'm afraid that you will not otherwise be able to use the Apple Watch. There is no way around this security feature.

Apple will not advise you of the previous owner's contact details (if different from the seller's), nor will Apple pass your details on to them.

More information:

About Activation Lock on your Apple Watch - Apple Support