Go and contact your cellphone provider they should go through the process of setting up your Apple Watch.
I was coming from the series 6 watch to the Ultra and was having problems setting it up. It was something like you can only have one watch paired to an Apple ID. Call them and ask them to help you setup up your new Apple Watch, they will. If you still get this error it is up to them to fix it. They might need to send you a new Apple Watch. Call them don’t go to your provider store. As I did and the person who helped me at the store did not know what she was doing. So much she ticked off the person at corporate and they hung up on her. I picked up my watch and went home and called my provider myself.
Like I said they will go through the process in setting up your Apple Watch. And if you still get this message it is up to them to fix it. If I remember right the EID number should be on the Apple Watch box. Lastly, there is no way for you to fix this on your own.