The 'Scheduled Msgs' menuitem can be found under the 'View' menu. This option allows you to make changes to a message that has been scheduled for delivery, but hasn't been sent yet.
To edit a scheduled message, highlight a message entry on the 'Scheduled Messages' screen and then hit the 'Edit' button. A message box will appear to let you know that this message will not be delivered until you hit the 'Send' button again (even if you don't make any changes). the data from the message you selected will be filled into the regular PageGate GUI Client screen. Make the necessary changes and then resend the message by hitting the 'Send' button.