Convert LOOP AT with modify to new syntax ABAP 750

[tejaspat2009]

Hello Team,

could anybody guide me to convert the below abap code to new syntax as per 750/740

Below the prepopulated (having 2 record line) internal table CT_ITEM has 40+ fields and we wanted to modify 1 field acctasscat. 

LOOP AT ct_item ASSIGNING FIELD-SYMBOL(<ls_ctitem>).

      IF line_exists( lt_ctitem-ariba_extension[ field_name = gc_asmtcat_name ] ).

          <ls_ctitem>-acctasscat = lt_ctitem-ariba_extension[ field_name = gc_asmtcat_name ]-field_value.

      ENDIF.

ENDLOOP.

I have tried doing it myself but no luck as its creates new record and that new records contain only one column filled. below is tried query

ct_item_tmp = VALUE #( FOR <ls_item_old> IN ct_item
LET lt_item = is_input-purchasing_contract_erpcreate-purchasing_contract-item[ ariba_item_id = <ls_item>-ariba_itemno ]
( acctasscat = COND knttp(
WHEN line_exists( is_input-purchasing_contract_erpcreate-purchasing_contract-item[ ariba_item_id = <ls_item_old>-ariba_itemno ]-ariba_extension[ field_name = gc_asmtcat_name ] )
THEN is_input-purchasing_contract_erpcreate-purchasing_contract-item[ ariba_item_id = <ls_item_old>-ariba_itemno ]-ariba_extension[ field_name = gc_asmtcat_name ]-field_value
ELSE space ) )
( <ls_item_old> ) ).

[Raghava11]

If this field acctasscat is primary key then it will insert new record

[tejaspat2009]

No its not primary key