Use FM CONVERT_DATE_TO_EXTERNAL to convert data from internal format, to user format.
FORM convert_date_format
USING
value(p_internal_format) TYPE datum
CHANGING
p_external_format TYPE char10.
CLEAR p_external_format.
CALL FUNCTION 'CONVERT_DATE_TO_EXTERNAL'
EXPORTING
date_internal = p_internal_format
IMPORTING
date_external = p_external_format
EXCEPTIONS
date_internal_is_invalid = 1
others = 2.
IF sy-subrc <> 0.
MESSAGE ID sy-msgid TYPE sy-msgty NUMBER sy-msgno
WITH sy-msgv1 sy-msgv2 sy-msgv3 sy-msgv4.
ENDIF.
ENDFORM.