Visit Fortnite Invite Event on iOS and click on Sign Up for invite event. Then Log in with your Epic Account or Create one if you dont have it yet.
Choose you Apple device in the next Menu. If you have an Android Device, this event is not for you. You might wait for some time until the Android Invite Event comes in.
Verify you Epic account and hooray! You are now a part of the event now! You will get a confirmation E-mail that will have a link to download the game from the App Store. You can download the app early also but cannot play until you recieve the mail.
So guys that is it for today and we will see you next time. Hope you get a Victory Royale!
Also check out Mobile Fortnite Controls vs PC controls.