In some cases, the Atlassian app might not be available via Atlassian Marketplace.
Some possible situations: app early access, QA/Staging/pre-production environment, troubleshooting session.
To install the app you must be in the administrator group.
Top menu bar > ‘Apps’ > ‘Manage your apps’ Settings > Enable private listings > Apply
Important: reload the page!
After page reload you will see the “Upload app” button that looks like a link.
Upload app > enter app url > Upload
Done. App should be installed.