Pairing Apple watch

You are experiencing Activation Lock on the Apple Watch. The previous owner did not remove the device from their account. Contact them and have them remove it. If you cannot contact them, then try returning the device for a refund, since it will not be able to be activated and is worthless to you. See this, About Activation Lock on your Apple Watch - Apple Support

Did you have the owner follow the steps listed in the support document that I provided the link for in my other post. That is how they need to remove the Activation Lock. The important section for them is if they don't have the Watch.

Turn off Activation Lock before you send your Apple Watch in for service, sell it, or give it away

Before you send your Apple Watch in for service, sell it, or give it away, you should turn off Activation Lock on your Apple Watch. Just unpair your Apple Watch from your iPhone:

1. Keep your Apple Watch and iPhone close together.
2. Open the Apple Watch app on your iPhone and tap the My Watch tab.
3. Tap your watch name at the top of the screen, then tap .
4. Tap Unpair Apple Watch. For Apple Watch Series 3 (GPS + Cellular), tap Remove [Carrier] Plan. If you aren't going to pair with a different Apple Watch or iPhone, you might need to contact your carrier to cancel your cellular subscription.*
5. Enter your Apple ID password. If you forgot your Apple ID password, you can reset it.
6. Tap again to confirm.

If you can't access your iPhone or Apple Watch, or if your Apple Watch isn't paired with your iPhone and you need to turn off Activation Lock:

1. On a computer, go to iCloud.com and sign in with your Apple ID.
2. Go to Find My iPhone.
3. Select All Devices, then click your Apple Watch.
4. Click Erase Apple Watch. Select Next until the device is erased.
5. Click next to your Apple Watch.

Unless you can get the original owner to remove the Watch from their account, it's useless to you.

As we have said, you don't. You have to have the previous owner do it, you cannot. If you have no information about them, then return the device to where you purchased it.