Update: here are my complete notes on migrating.
https://gist.github.com/ianchesal/5c96c566ab99b60c2c557711fa...
I thought they were in the other comment. The migration is pretty simple now that heroku only hosts the static part of the site and the data is in Atlas.
I mentioned the guide and my work on the NightScout discord. If there’s interest I could do from scratch instructions for those doing entirely new setups.
Note: I’m the person who did the migration and wrote the notes linked to above.