Ender's Game is already done filming. Also it is fictional. On top of that, I'm pretty sure Harrison Ford only wants genius children in his army of alien killers. So when I say you are unlikely to join the film's International Fleet, I feel pretty confident in my words.
Nevertheless, Lions Gate and Summit Entertainment have put together a social media game which allows you to take an aptitude test which may gain you entry into the film's military unit. I did not play the game, so I don't know if it's any fun. I can tell you that when you click on a different browser tab, the game's music automatically mutes. This could be the greatest technological marvel mankind has achieved.
You can play the game here. If any of you check it out, please tell us what you find. And if you DO get to join the fleet, good luck. Be nice to Bean.