How to use Field Conditions in Payment File Structure

Hi experts,

          Please sobody kindly explain how to use this.

          I need to asign dynamic values to the fields.

           e.g  if the payee bank is from Europe, I want to set EU to MsgToPayee field or if the payee bank is from other countries, I wan to set Other to MsgToPayee field.

Special thanks in advance.

Best Regards,

Fred