When you first turn on the new Chromecast with Google TV, you're put through an extremely simple setup process: choose your language, connect to Wi-Fi, log in to Google, select your default streaming apps. There's not much to it, but just in case Google wants to change things around, the tool is now on the Play Store.
There's not much to this, and most users won't ever need to actually visit the Play Store listing to update the app. It should download to the latest Chromecast (and any other Android TV devices with the Google TV interface) automatically, and update as needed. I suspect that Google's main drive for putting this APK up on the Play Store is so that it can add and remove streaming services from the final step; for example, replacing CBS All Access with Paramount+.
In any case, it's there on the Play Store if you need it. We're also keeping track of the releases over on APK Mirror, as usual.