The BIC code is automatically entered according to the IBAN. It is impossible to modify it.
From the 01/02/2016 on, for the SEPA transactions, the BIC code is not mandatory on mandates.
The date entered in the parameterOPTBICSTR - Optional BIC start date(TC chapter, SDD group) determines whether you can leave the field BIC code empty in the mandate, based on the mandate creation date.
If the parameter value allows to leave this field empty, you can validate the mandate (from the button Validation, or from the function of Mandate validation (VALMDT).