Customize the public action Manually Assign Order Release to Existing Shipment

Hi All,

I have a requirement for my customer where there is a action button "Manually assign Order Release to Existing Shipment" in ORder release screen. This is a public action.

Now Customer wants to revise the actions performed through this action button like copying some refnums etc apart from its usual functionality.

I am trying to customize this action, by linking this action to an agent but not sure what will be the agent action in this case to do the same functionality as Manually assign ORder release to exiosting shipment.???

Please advise.