What you want to do, methinks, is install a new discourse from scratch, copy your backup file into the backups folder, then restore the backup via the web interface. It will then bring back your site.
You will need to set up your app.yml again to match what you had previously. In the future, whenever you make a change to your app.yml file you want to copy it to your local so you can easily recreate it again next time.
You do do not want to mess with the tar.gz backup file yourself. Let the discourse backup/restore do the heavy lifting.
(I just did a quick search for a restore from backup #howto topic but didn’t find one - maybe someone else can direct you to the right place to inform yourself further on how the backup/restore process works…)