You bought a useless Apple Watch you cannot use. If you can't reach or don't know the person whose ID the watch is actually locked to, there is NO WAY you can EVER use the watch. Apple will NOT help you. We cannot help you.
Either get the person (if they are actually the real owner you bought the watch from) to remove the watch from their account or recycle the watch responsibly. As it is, it is utterly useless to you or anyone else.
Read this about buying used devices --> The All Too Common SAD Reality of Buying … - Apple Community