Hi
You are describing Activation Lock, which prevents unauthorised use of a pre-owned Apple Watch if it is lost or stolen.
I suggest that you return the Apple Watch to the store to have them remove the lock or to obtain an exchange or refund.
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, nor will Apple pass your details on to them.
More information: