and "octava bassa" 
you will find in the toolbar - category < Clef / Key >.Set Octave Pitch Position ("octava alta"And "octava bassa")
The buttons "octava alta" and "octava bassa" you will find in the toolbar - category < Clef / Key >.
Mark the area, for which the changed octave pitch-position is in force.
Afterwards, click on the corresponding button.
Signs of octave pitch-position are symbols and are also handled like Symbols