You can see these controls at the bottom of the screen. When you are in the replay mode, you can record the Fortnite gameplay based on your need. The Fortnite replay mode allows you to custom the camera angle, change the video speed, skip around the recording, and tweak the visuals and more.
When you get there, you can see a list of recent games and unsaved Fortnite replays. To find and access the Fortnite replay functionality, you should go to the Battle Royale menu, choose the Career tab, and then select the Replays option. So you can only use this Fortnite replay mode on your computer or game console to capture game playing. But the Fortnite replay mode is not available on mobile phones for now. You can play Fortnite games like Save the World, Fortnite Battle Royale and Fortnite Creative on Sony PlayStation 5/4, Nintendo Switch, Xbox One, Windows PC, Mac and iOS/Android devices.