BAPI or FM to update IBAN and email of a customer

Hi,

     I am creating a RFC function module where I need to update the IBAN (International Bank Account Number) of a customer in XD02 or table KNBK.

In the FM I am importing customer number, IBAN and email . The value of IBAN which I am giving as input must get updated against that customer(importing) in table KNBK or XD02.

But my problem is I am not getting any FM that will update the IBAN against that particular customer in XD02.

I have used few FM like  CONVERT_IBAN_2_BANK_ACCOUNT, CONVERT_BANK_ACCOUNT_2_IBAN, BAPI_IBAN_CHANGE and many more but none is updating the value with the new input value.

Same problem is with email address when I am trying to update. No FM I have found to update email.

So plz can u help me as how to update IBAN and EMAIL.

Thanks

PP