Hello Lim,
You may not have this field in this fm, because this fm is related to Order and your requirement is about a field related to associate Notification. This field is appearing in Order Header because of the spro settings made in Order-Notification integration.
But there is a way. You can get this field updated through F/Exit EXIT_SAPMIWO0_020 (user-exit QQMA0014).
Suppose the Notification type that is created is of 'M2' type, then put these lines in the include ZXQQMU20 of this exit.
IF i_viqmel-qmart = 'M2'.
e_viqmel-qmnam = sy-uname.
ENDIF.
This updates the 'Reported by' field of the Notification with the name of the logged in user. If you want it to be filled through some value other than system user, then modify the syntax accordingly.
Good luck
KJogeswaraRao