Updating serial number in IE01 .

Hello experts,

               I have a requirement where in   IE01  if sernr is not provided in serial number tab  I need to  generate a customized serial number  . For this  I am using exit  "IEQM0003 "  . Once I generate the serial number how can i display the generated serial number in the respective field on screen .

Thanks and regards ,

Prakrita Kapoor.