After you have finished with pervious 3 steps, in the folder that you get from CodeCanyon there is folder "DemoData". 

There you will find file "demodata.json".
Go in your Firebase Console 
Open your project and go in "Database", and select "Realtime Database"

On the "More" icon on left, click on "Import JSON".
Select the "demodata.json" file. This will insert the demo data (in fact only the design for your app )inside your firebase.

That's it. The admin panel is set up. 

You can view videos of the admin panel in action to see how it works.

Next, you can publish the admin panel. 

To do that follow this guide.