@ShellyE
The QR code and the 6-character alphanumeric setup code are both printed on the back of the 1st gen Google Nest Hello Doorbell. (We have three of them.). You need one or the other to reinstall the doorbell. For years, we've made a habit of writing down the 6-character alphanumeric setup code for each of our cameras and doorbells.
See the video in the Help topic below, starting at about 2:20:
https://support.google.com/googlenest/answer/9247327
