Unfortunately, the Fusion repository is no longer available, so it is not possible to install it on Kodi 17.3 or any other version of Kodi. The Fusion repository was shut down by its developers several years ago due to legal issues and has not been resurrected since then.
In the past, the Fusion repository was a popular source for a variety of Kodi add-ons, including Exodus, Indigo, and many others. However, as it is no longer available, users will need to find other sources for their Kodi add-ons.
There are several alternative repositories available for Kodi that provide access to a variety of add-ons, such as the Kodi Bae Repository, the Superrepo Repository, and the Kodil Repository, among others. Users can search online for guides on how to install these repositories on their version of Kodi.
It is important to note that while Kodi add-ons can be a great way to access a variety of video content, some add-ons may provide access to pirated or copyrighted content. It is important to use caution and research any add-ons before installing them on your Kodi system.