1. In Dorico, there is no penalty for changing your mind. If you decide that the first bar of your piece should be a pick-up bar, it is very easy to edit.
  2. Remove the unwanted time at the beginning of the first bar. You can do this either by using the System Track (hold down Alt/Option in order to be able to select beats rather than bars), or by using the Shift+B Bars and Barlines popover. The syntax for removing time is a minus sign followed buy a number and the unit (q = quarter note, e = eighth note and so on).
  3. Edit the time signature/meter to include a pick-up bar by double-clicking it, and adding the number of beats the pick-up should have after a comma.
  4. It doesn’t matter which order you perform these two actions.