As a user: The user who has the item in the inbox has to set up a substitute. The substitute can then process the other user’s work items.
You have a choice of two different substitute rulings:
Active substitute ruling (for example, for absence due to vacations): In this case, the items belonging to the absent person are automatically assigned to the substitutes inbox (in addition to his own work items).
Passive substitution (for example, for absence due to illness): the substitute must explicitly assume the substitution and can only view the items of the absent person in this mode.
As an administrator: Transaction SWIA
Programatically: Function module SAP_WAPI_EXECUTE_WORKITEM
Workflow : Other Useful Links :
Org units in workflow steps?
‘No Administrator found’ workflow error
LIV & Payment Release workflow
Workflow performance tips
Viewing another user’s workflow inbox
How can I temporarily disable a workflow in production?
Raising ABAP OO events for workflow