The SBS On Demand app is available on Amazon Fire TV devices running Fire OS 5 and above. The app does not come pre-installed on these devices and must be downloaded from the Amazon Appstore.
You will need an Amazon Account in order to perform the following. On the Amazon home screen, select the orange "appstore" icon. Then:
Select “All Categories”, then choose “Entertainment”. A list of applications will appear.
Locate the SBS On Demand app (it should appear next to ABC iview) and select it.
Select "Install" or "Download" to add the application onto your device.
You can detailed instructions on how to sign into the application using your email address, password or directly through a QR Code here: How do I connect my smart TV to the SBS On Demand app with a QR Code?