How to change the title of iPhone memories photos

You can edit the title, while memories being played.

See: http://help.apple.com/iphone/11/#/iphd4f70e68f

Customize a Memory movie. Tap a Memory movie while it’s playing, then tap Edit to do the following:

• Edit the title: Tap Title, tap the title and subtitle to edit them, then choose a title style.
• Choose a title image: Tap Title Image, then tap the photo or video you want to use.
• Choose different music: Tap Music, then choose music from a soundtrack or from your music library (only music you own that’s stored on iPhone is available).
• Choose a custom duration: Tap Duration.
• Choose photos and videos: Tap Photos & Videos, tap ,then tap the photos and videos you want in the movie. Deselect photos and videos currently in the Memory movie to remove them.