To find a game you purchased on the Quest, there are a few places to check.
The first place being the game library, please make sure all filters are enabled so no games are hiding - you can then sort A - Z to help find the game faster.
You can also visit the store page for the game to press play from there, that may force your headset to find the game if it hasn't automatically for any reason.
Finally, you can try installing the game from the Horizon mobile app. Ensure you're signed in to the same account you made the purchase on.
If trouble continues, please contact us, and we'll assist further!