datatable old data erase when second time foreach loop execute

my datatable old data erase when second time foreach loop execute

when second time inside foreach loop then my old data is erase

Code :

private void btnTodayUrgent_Click(object sender, EventArgs e)
{

    if (mStrSelLotCodeList != "")
    {
        //if (true)
        //{

        //}
        //DataGridViewCellStyle style = new DataGridViewCellStyle();
        //style.ForeColor = Color.Red;
        string[] StrColumns = mStrSelLotCodeList.ToString().Split(',');
        foreach (string Str in StrColumns)
        {
            //DataTable dt1 = new DataTable();
            //dt = dttableOld.Clone();
             dt = ObjBOPelAdmin.DS.Tables[ObjBOPelAdmin.StrPacketMastFill].AsEnumerable().Where(X => Val.ToString(X["LOT_CODE"]) == Str).CopyToDataTable();
            dt.AcceptChanges();
            //dt = c;
            //dt.Rows.Add(c);
            //var dataRow = dt.NewRow();
            //DataRow row = dt.NewRow();
            //dt.Rows.Add(dt1.Rows);
            //dt.ImportRow();
            //dt.Rows.Add(dt1);
            //dt.ImportRow(dt1);
            //dt.Rows.Add(dt1);
            //dt = dt1.Clone();
        }

need help