Log into your Jira instance as an admin.
Click the admin dropdown and choose Add-ons.
The Find new apps or Find new add-ons screen loads.
Click Free trial to download and install your app.
You're all set!
Click Close in the Installed and ready to go dialog.
Go to a project and click "Fast Gantt". If the project it not yet configured, you will get to the settings page.
To enable the project. Press “Enable FastGantt for Project”
Once the project is setup a “Back to Gantt” button will be visible.