In order to re-connect Nest to Stringify, please follow these steps:
Login to https://home.nest.com and click on the Settings icon in the upper right.
Choose 'Works With Nest' then find Stringify. Click on it then revoke access for Stringify.
Within a few minutes, All Nest icons in the Stringify app should have a (!) next to them. Click on the Nest 'Home' icon to re-connect to Nest.