Hi,
Try to do it with TRANSLATE function:
export the output of below command in IXF format and then Import the same with replace_create option, this can work for you
syntax:
select field_name1,field_name2,
translate(field_name3,'AaBbCcDdEeFfGgHhIiJjKkLlMmN nOoPpQqRrSsTtUuVvWwXxYyZz', 'zZeEbBrRaAsScCdDfFgGhHiIjJkKlLmMnNoOpPqQtTuUvVwWx XyY') ,
translate(field_name4,'AaBbCcDdEeFfGgHhIiJjKkLlMmN nOoPpQqRrSsTtUuVvWwXxYyZz', 'zZeEbBrRaAsScCdDfFgGhHiIjJkKlLmMnNoOpPqQtTuUvVwWx XyY') , field_name5 from table name
regards,
Harsh