The previous owner has to remove the doorbell from their account in the Google Nest app or the Google Home a..
This is what Google Nest says if you're getting the "...connected to another account" error message:
"If you bought this camera new or can’t get the previous owner to remove the camera from their account, return it to the seller for a refund or exchange it for another. Let the seller know that your product is already connected to someone else’s account and it can’t be set up."
You could try contacting Support (https://support.google.com/googlenest/gethelp), but I don't know if they can resolve it.
@Windtalker thanks for posting here in the Community. Were you able to read the information and check the link that MplsCustomer has shared? Also, could you still contact the previous owner and check if they can still have access to their account? In case you have an update, you know where to find us.
I appreciate the response, MplsCustomer.