Press "Edit" button in course element "Notification" (Mitteilungen):
- Open a course which includes the element "Notification".
- Create a new notification with an attachment.
- Click on the "Edit" button.
-> OK: The text of the notification can be edited.
-> NOK: The attachment can not be edited. It actually is not visible in the edit mode.
Clicking the "Edit" button should allow you to change the text and the attachment.