https://www.gamespot.com/articles/how-to-get-fortnite-mobile-on-ios/1100-6457329/

Epic recently announced that it is bringing the massively popular free-to-play game Fortnite: Battle Royale to iOS and Android devices. Prior to its official mobile launch, however, it will conduct a test on iOS to put the game through its paces. This won't be open to everyone, but sign-ups for the invite-only trial are now open on Epic's official website. [Update: Fortnite mobile is now live and invites are going out.]

Both iOS and Android users can sign up for the trial, but only those with the former devices will be able to participate for the time being; Epic says Android support will follow "in the next few months." Players will need an internet connection and an iPhone 6S/SE, iPad Mini 4, iPad Air 2, iPad 2017, iPad Pro, or a newer Apple device with iOS 11 in order to play the game. For an idea of what to expect, you can check out the first Fortnite mobile gameplay video.