Sign-up here…
What other steps you need to take will depend on your existing projects and code.
With your code, it could be as simple as adding a couple of lines to the top of the sketch and inserting the new Auth token, but it’s impossible to say based on the information you’ve provided.
As far as the web console and app are concerned, you will need to create a template (or possibly three) and datastreams for each template, then create your devices from those templates.
This will give you the additional lines of code and new Auth token to copy to the top of your sketches. I’d suggest that you do this in the web console, then set-up the new app to mimic your existing app.
You’ll need to upload new sketches to each of your hardware devices.
Pete.