There is no need to download the extension for Qlik.
The Qlik extension is installed using the Qlik Management Console (QMC), which is typically owned by a company's administrator. If the extension has been set up properly by the admin, you should just see it available to you in-tool as a Custom Object called "Narratives" and you can drag that into your chart.
If you do not see that, it's probably an indication that the extension is not available based on your permissions or something else to do with the set-up. We would recommend reaching out to your Qlik admin for support.