I set up with email account that no longer exists.
If the account no longer exists, highly unlikely you can recover the account. I'd recommend factory resetting the thermostat, and set it up again with a new account.
Restart or reset a Nest thermostat - Google Nest Help
Check which model of thermostat you have:
How to tell which Nest thermostat you have - Google Nest Help
Nest Thermostat
For the Nest Thermostat model, use the Google Home app. The QR code and setup key are physically printed on the back of the thermostat. Follow these steps:
Get started with your Nest Thermostat - Google Nest Help
Nest Thermostat E and Nest Learning Thermostat
For Nest Thermostat E and Nest Learning Thermostat models, use the Nest app. The QR code and setup key are in the settings on the thermostat itself and are not printed on the device. Follow these steps:
Add your Nest thermostat to the Nest app - Google Nest Help
