Apple tv 3rd or 4th generation and HBO NOW

HI everybody! I just bought an apple TV 3 to watch HBO NOW. But I didn't succeed to find the HBO NOW button in menu. I did an ipdate but even then the button didn't showed up. I just bought apple tv 3th generation in a Belgium apple store just and only to get acces to HBO now contents. I'm a big fan of Games of Thrones and the only way to watch this is by HBO NOW. But I didn't succeed to find the HBO NOW application on my menu screen. Even after an update the app didn't show up. So please, can you give me any advice how a installate the HBO NOW button on my apple TV? I live in Belgium and I have no cable TV.
Please can you help me?
Thank you so much,
Joyce