Scroll through the options at the bottom of the screen and tap Audio > Voiceover.
The Voiceover control panel opens with an audio meter and a large red record button.
Tap the red button to begin. A countdown from 3 to 1 appears before recording starts.
Your video plays back as you record, helping you sync your voiceover with the visuals.
Tap the red button again to stop. Your recorded voiceover is automatically added to the timeline for further editing.