How do I change an entry to a different date? What if I don't know the exact date?

Tap on the entry, then tap the "Edit" button. (Note that you cannot edit entries written by someone else)

Tap the date to change it. 

You can change the date here. If you don't know the exact date, tap "Approximate date" 

When the timeline is refreshed, the entry is moved to the new date.