In the Piano Roll Editor menu bar, tap the Trim button .
Tap a note to select it, or select multiple notes.
Trim handles at the start and end of the note will appear. Depending on the note length, you might need to zoom in to the working area to make the handles visible.
Touch and hold one of the handles and drag it left or right.
Dragging the left handle will change the start position of the note and its length. Dragging the right handle will change the length of the note without changing its start position.
With the Pencil button selected, you can drag the left or right edge of a note to trim it even though there are no trim handles visible.
Tip: When you wait for a second after you touch and hold the note, the working area zooms in horizontally to let you adjust the start or end point more precisely.