Depending on what you’re bringing over, it might be easier if you run fly launch from the root of your NodeJS project (and not go through the Web GUI) and follow the instructions for bringing over your pg database at Migrate a Postgres Database from Heroku · Fly Docs.
There’s a few steps in the Rails migration docs at Migrate from Heroku · Fly Docs that might be helpful for bringing your NodeJS app over, but obviously not everything is applicable.