You don't indicate what happened before, so here's a guess at one possibility. If you change your Wi-Fi network name (SSID) and password, Google Nest's recommended process is to remove your Google Nest device(s) from the Google Nest app or Google Home app while still connected to your old Wi-Fi network, then do a factory reset, and then re-install while connected to your new Wi-Fi network. If you fail to perform the first step, then you can get an error message saying your Google Nest device is already connected to another account; the install process does NOT check WHICH account the device is attached to, and seems incapable of recognizing that it is connected to YOUR account.
If this is your situation (https://support.google.com/googlenest/gethelp), you may need assistance from Support to get past Google Nest's roadblock.
@LarryL thanks for posting here in the community. Let's go ahead and see what's going on. A few questions: what type of Nest Doorbell do you have? Are you trying to set it up using your Nest app or Google Home app?
Keep us posted.
I appreciate the help, MplsCustomer.