Error while selecting into field-symbol in SAP ABAP

The problem is that you have not declared Field-symbol. Try using the below code.

data:  ws_bkpf      TYPE bkpf_type.
SELECT MANDT
   INTO CORRESPONDING FIELDS OF ws_mandt UP TO 1 ROWS
   FROM bkpf
   WHERE belnr = '1700001016'.
ENDSELECT.