Quick Fill is the fastest way to fill a whole month at once on iOS. It looks at the date each photo or video in your library was taken and lines it up with the matching day in your project. It only fills days that are still empty—snippets you've already created aren't touched.
Quick Fill is available on iOS. On Android, use Auto-Fill. To fill a single day from its context menu, use Autofill instead.
Steps
Open a project and tap the yellow Quick Fill button near the bottom of the calendar.
Pick a month. Each card tells you how many videos are available and how many days would be filled.
Watch the preview. Quick Fill plays the snippet it chose for each empty day.
Tap Edit to change what it picked, or Add to Project to keep them.
That's it! The snippets appear on their days in the calendar. If a month isn't offered, your library has nothing from those dates, so there's nothing for Quick Fill to place—tap a day and add a snippet by hand instead.
The first time you open Quick Fill it introduces itself and offers the month it rates highest—tap Show me a preview to go straight there. After that you get the month list, unless only one month has anything to add.
Nothing is added until you tap Add to Project, so you can back out at any point with Cancel.