Scheduling after Activity Confirmation in SAP S/4HANA

Hi experts, 

We person a occupation with task scheduling. aft existent confirmation for activities and docket project, WBS dates are re-scheduled and commencement with the commencement of activities without confirmation. our script is bottom-up and we don't privation to usage top-down. How tin we usage the activity's existent commencement day for the WBS basal commencement date?
The representation beneath shows this problem.