Dorico Pro automatically selects octaves during note input, but you can override this and select octaves manually.
During note input, Dorico Pro automatically selects notes with the smallest interval away from the previously input note. For example, if you input an F and then press A, an A is input a third above the F, rather than a sixth below.
You can override this automatic octave selection in the following ways:
Octave selection when inputting chords
During chord input, Dorico Pro automatically inputs notes above the highest note at the caret position. For example, if you press A then E then A, a chord of A-E-A is input at the caret position.
You can input notes below the lowest note at the caret position instead by pressing Ctrl-Alt (Windows) or Ctrl (macOS) as well as the letter for the note name; for example, Ctrl-Alt-A (Windows) or Ctrl-A (macOS).