"Please use the Epic Games Launcher to start game. Connection to the internet is required." error message

To resolve this error message, try deleting the .egstore folder. This will sever the connection with the launcher. If the launcher fails to detect the game, you may need to reinstall it.

1. Go to Epic Games Library
2. Go to the game that's leading to the error, and click the 3 dots next to the title
3. Select Manage
4. Select the folder next to Uninstall to open the file location
5. Delete the .egstore folder. 
6. Restart the Launcher and relaunch the game
   Note: You can try connecting the Epic Games Launcher to the existing installation, following Can the Epic Games Launcher detect previously installed games?