I have my old Apple Watch but I don’t remember my email connected to it nor have the same phone number
How can I factory test my watch to wear I can connect my new phone
Try these things:
And this:
If you forgot your Apple ID email address or phone number - Apple Support
Past that, you are going to need to show Apple proof of ownership.
You'll need a receipt for the watch and the receipt HAS to show the serial number.
https://getsupport.apple.com/?caller=psp