You can add notes to an existing annotation if the task's status is not set. If you have a user right to view other user's annotations, you can add notes to an annotation added by another user.

1. Click the annotation to which you want to add a note.

2. To expand the annotation box, click anywhere in the annotation box.
3. Click the + button.
4. In the text dialog box that appears, type the text of the note, and click Done.