If you have an external hard drive connected to your Xbox One, make sure you are looking for the game in the right place.
- Push the guide button on your Xbox One controller
- Navigate to the settings tab via the side bar
- Select the "all settings" option
- Scroll down the side bar to "system"
- Navigate to the "storage" option
If you can see more than one storage device, then there is more than one place your game could be installed.
- Go to games & apps
- In the top right-hand corner, you should see "storage device"
- From this drop down and make sure "all" is selected
If you have downloaded and installed the game correctly onto you internal or external hard drive, it should now be visible in your available games.
If you still cannot find the game, check your uninstalled games and download queue. If the game is in either of these queues, then it hasn't installed successfully, and you will need to wait until this process has completed.
If you're still having trouble with your console you can contact Microsoft directly for support