On the trip detail Map screen, first tap the day you want to edit. Tap Edit, then tap the + button to add places to that day. After you add at least one place, drag the reorder handle (hamburger icon) on the right side of the list row up or down to reorder. While Edit mode is active, you can tap Add Day to add a day, or Delete Day to remove a day, allowing you to shape the itinerary exactly how you want.