Hi we can use ToLower Method sometimes it is not filter.
EmployeeId = Session["EmployeeID"].ToString();
var rows = dtCrewList.AsEnumerable().Where
(row => row.Field<string>("EmployeeId").ToLower()== EmployeeId.ToLower());
if (rows.Any())
{
tblFiltered = rows.CopyToDataTable<DataRow>();
}