select 'x', a.gd_gm_id, ...
into v_check, vid, ...
from store.grn_detl a
...

declare
  cursor c1 is 
    select gd_pom_id, gd_po_date, gd_challan_no, gd_challan_dt, gd_cim_icode,
           gd_cuom_ucode, gd_qty, gd_pom_no, gd_status, gd_serno, gd_req_serno,
           gd_gm_id		   
      from factory_data.grn_detl 
      where nvl(gd_status,'O') = 'O' 
      order by gd_gm_id, gd_serno;
  rec   c1%rowtype;
  vid   factory_data.grn_detl.gd_gm_id%type;
  vsno  factory_data.grn_detl.gd_serno%type;
  vcode factory_data.grn_detl.gd_cim_icode%type;
begin
  for rec in c1 loop
    begin
      select a.gd_gm_id, a.gd_serno, a.gd_cim_icode
        into vid, vsno, vcode
        from store.grn_detl a
        where a.gd_gm_id = rec.gd_gm_id
          and a.gd_serno = rec.gd_serno
          and a.gd_cim_icode = rec.gd_cim_icode;
			
      update store.grn_detl
        set
          GD_POM_ID      = rec.gd_pom_id,
          GD_PO_DATE     = rec.gd_po_date,
          GD_CHALLAN_NO	 = rec.gd_challan_no,
          GD_CHALLAN_DT	 = rec.gd_challan_dt,
          GD_CIM_ICODE   = rec.gd_cim_icode,
          GD_CUOM_UCODE	 = rec.gd_cuom_ucode,
          GD_QTY         = rec.gd_qty,
          GD_POM_NO      = rec.gd_pom_no,
          GD_STATUS      = rec.gd_status,
          GD_SERNO       = rec.gd_serno,
          GD_REQ_SERNO   = rec.gd_req_serno
        where gd_gm_id = rec.gd_gm_id;

    exception
      when no_data_found then
        insert into store.grn_detl
          (gd_gm_id, gd_pom_id, gd_po_date, gd_challan_no, gd_challan_dt, gd_cim_icode, 
           gd_cuom_ucode, gd_qty, gd_pom_no, gd_status, gd_serno, gd_req_serno)
          values
         (rec.gd_gm_id, rec.gd_pom_id, rec.gd_po_date, rec.gd_challan_no, rec.gd_challan_dt, rec.gd_cim_icode, 
          rec.gd_cuom_ucode, rec.gd_qty, rec.gd_pom_no, rec.gd_status, rec.gd_serno, rec.gd_req_serno);

      when too_many_rows then
        insert into store.grn_detl
	  (gd_gm_id, gd_pom_id, gd_po_date, gd_challan_no, gd_challan_dt, gd_cim_icode, 
	   gd_cuom_ucode, gd_qty, gd_pom_no, gd_status, gd_serno, gd_req_serno)
          values
	 (rec.gd_gm_id, rec.gd_pom_id, rec.gd_po_date, rec.gd_challan_no, rec.gd_challan_dt, rec.gd_cim_icode, 
	  rec.gd_cuom_ucode, rec.gd_qty, rec.gd_pom_no, rec.gd_status, rec.gd_serno, rec.gd_req_serno);
    end;
  end loop;
end;