Choose Window >
Advanced Tools. Click the Special Tools tool , and click the measure
in question.
Click the Reverse Stem Tool . A handle appears above and below each note or chord.
Click the upper handle (for an upstem note),
or the lower handle (for a downstem note). Finale responds by attaching
the stem to the opposite side of the notehead. Bear in mind that you should
decide which handle to click (upper or lower) based on the stem’s direction.