I’m trying to remove the activation lock from a used iPhone watch

You can't without the correct Apple ID & password.

Activation Lock is a theft deterrent feature with no bypass or workaround.

Without the owner's authorisation (Apple ID & password), no thief or anyone including you can re-use the device.

there are people on eBay that can remove that

also.... if you bought the watch from specific websites you can get 30 day money back