iMovie: need song to start in middle, always starts at beginning

I'm adding an audio clip using the iMovie app on my iPhone 5S. It's a song & I need it to start in the middle of the song, but it always starts at the beginning no matter how much I play with it. How do I resolve this?

Note: I do not own a Mac, just the iPhone. So I have no other alternative than to use the app on the iPhone iOS.