There are two ways to split an audio clip in a movie project. When you split a clip, you can remove unwanted sections, or adjust the duration, volume or speed of each section.
In the iMovie app on your iPhone, open a movie project.
Scroll the timeline to position the playhead where you want to split an audio clip.
Tap the audio clip in the timeline to reveal the inspector at the bottom of the screen.
Tap the Actions button , then tap Split.
Alternatively, you can tap the clip (it becomes outlined in yellow), then swipe down over the playhead to split the clip, as if you were using your finger to slice through it.