If you have the newer 2nd Gen Google Nest Doorbell (wired), it works only in the Google Home app.
You could try a simple restart by briefly turning off the electrical circuit that includes your doorbell. We've done that a couple of times with one of our older Google Nest Hello Doorbells to resolve other issues.
If that does not help, you could try the "restart" documented on the link below, but you have to dismount your doorbell for that:
What happens if you try to access your doorbell's camera on the "preview" website, home.google.com?