SAP CRM Search Help - defaulting values in search help screen

Hi All,

I am working on search help object in service order(Amount allocation )  BTAMNTALL component view name vIEW:BTAMNTALL/HdrBillplanDet and field name STRUCT.AC_ASSIGNMENT. in that block if we select account assignment type as ERP cost center it will give standard search help in Select account assignment field.

Its basically calling the standard search help CRMT_AC_ASSIGN_KOSTL_E. After pressing F4 it will display the popup Controlling area cost center and description. Basically I need to default the Controlling area in F4 help based on some logic.I am not sure where to write code for this one.

Please find the attachment where I need to default the value. any help is appreciated.

Thanks,

Sapsar.