it is the app where you play the game you have to download it. They should ask you t download it before creating an account if not you should be able to find it on their website. Feel free to use my referral code also if you want if not it is okay!
Sign up using with my referral code: qJHOnBuyTK on the website here https://godsunchained.com/account/register?referral=qJHOnBuyTK
And if you did not find where to download it here you should find the "Play now for free" button which makes you download it https://godsunchained.com/