Visit the Dev Console: Twitch Developers
Manage the extension
Manage a version of the extension
Click “Asset Hosting”
You can define the views you want to enable on your extension
And the paths/files for the HTML you want to use
Then in the Rig under “Project Details” click “Refresh Manifest” to reload the updated values from the console into the rig.
Then the Rig is now aware of what enabled views you have and what files to load for those views.
The Testing Base URI defined here is overriden when you use “run front end” when using a folder of files so this setting is irrelevant for you.