How do I edit the first message of a ticket?

Open the options menu (the three-dot icon) on the ticket's first message and choose "Edit". Make your changes in the editor and click "Save Changes", or "Cancel" to discard them. The content cannot be saved empty ("Content required"). Editing is only available when the message was written in Deskhero; the Edit option is disabled for tickets that arrived as email, because the original email content is preserved as-is.