If you have notes in a split track they can be assigned to either the
treble or bass staff.
Select the note(s) you want to assign to one staff or the other and choose Staff from the edit menu. Select Bass from the submenu to move the note to the bass staff. Select Treble to move the note to the treble staff. Select Default to move the note to the treble staff if it is greater than or equal to middle C, or to the bass staff if not.