Hi Suneel!
Why you are using the field symbol! If you don't know how to use the field symbol don't use it.
Make sure that your total program has to work with field symbols or work areas. don't mix up the things.
Please change your code as mentioned below! let me know if you have any problem.
FORM apserv_itab .
DATA:l_data TYPE string.
p_file = '\\dj56bi00v\migration\migration\CSVManual\suneel.txt'.
OPEN DATASET p_file FOR INPUT IN TEXT MODE ENCODING DEFAULT.
IF sy-subrc NE 0.
MESSAGE 'UNABLE TO OPEN THE FILE' TYPE 'I'.
ENDIF.
DO.
READ DATASET p_file INTO l_data.
IF sy-subrc = 0.
SPLIT l_data AT cl_abap_char_utilities=>horizontal_tab INTO wa_zdsl-mandt
wa_zdsl-werks
wa_zdsl-pallet_id
wa_zdsl-matnr
wa_zdsl-erfmg
wa_zdsl-uom
wa_zdsl-lgort
wa_zdsl-lot
wa_zdsl-prod_date
wa_zdsl-ebeln
wa_zdsl-erdat
wa_zdsl-erzet
wa_zdsl-ernam
wa_zdsl-aedat
wa_zdsl-username
wa_zdsl-floc.
move-corresponding wa_zsdl to wa2.
move wa_zsdl-erfmg to wa2-erfmg.
append wa2 to me_zdsl.
append wa_zdsl to it_zdsl.
clear: wa2,
wa_zdsl.
ELSE.
EXIT.
ENDIF.
ENDDO.
ENDFORM. " APSERV_ITAB