Hi Shiva,
As a starting point, please proceed with running your transaction in SAP after switching on the event trace(SWELS). After that, check if any standard event is triggered or not in SWEL.
If there is no standard event, please use business object BUS1001006 to create the subtype of it and make your custom event inside the same.
Then,continue with the design of workflow in SWDD.
Richa