To service a message back to the Originating Station requires you to send a properly formatted message to the sender. A properly formatted message is one that conforms to the NTS/ARRL/Universal Radiogram format.
A Service Message can be as simple as:
[Msg. #] R W7ARC ARL6 LYNNWOOD WA [date]
ARL SIXTY SEVEN [message #] PHONE
This should be the minimum message sent as a Service Message. DO NOT just come back to the net and say, "I couldn't deliver the message to..." this is not acceptable and only adds to the confusion of the net.
If you have questions or need further instruction you can contact: firstname.lastname@example.org.