That will be down to the OS, or drivers.
It's down to the user to mark that application as something to run on the dedicated GPU using the right software (like NVidias control panel), or to the driver developers to add the game to their list of games to run on the high performance card.
To be honest though, a 2D game is expected to run on integrated graohgra and if you are getting performance issues you should consider optimizing your game.