Add titles to a trailer in iMovie on iPhone
After you create a trailer project and choose a trailer template, you can customize the movie name, cast members, credits, and titles. All of this information appears in your final trailer.
Add movie information
With your trailer open, tap the Outline tab.
Tap the placeholder name in any field, then type new text.
In the Studio Name field, type a fictitious name, then tap Done to dismiss the keyboard.
To change the studio logo style, tap the logo style name, and tap a different logo style.
If applicable, tap a cast member’s gender and title style to select different ones.
If the template allows for a variable number of cast members, tap the Add button
or the Remove button 
to add or remove cast members.
Add your own titles
With your trailer open, tap the Storyboard tab.
Tap any blue bar to make its text fields editable, then type new text.
To edit another title, tap the Previous button
or Next button 
above the keyboard.You can tap the Clear button above the keyboard to quickly empty all text fields.
When you’re finished making changes, tap Done on the keyboard.
To restore a title to its original text, tap it, then tap the Revert button above the keyboard.
To bring your trailer to life with video and photos, see Add video and photos to a trailer in iMovie on iPhone.