You are better of using DataTable.Select
method, but if you have to use LINQ then you can try:
DataTable selectedTable = tb.AsEnumerable()
.Where(r => r.Field<string>("Modul") == value)
.CopyToDataTable();
This would create a new DataTable
based on filtered values.
If you use DataTable.Select
string expression = "Modul =" + value;
DataRow[] selectedRows = tb.Select(expression);