Please go to this example to see which plugins you need:

https://datatables.net/extensions/buttons/examples/initialisation/export.html

Then go to this page to download DataTables.min.js with previous plugins:

https://datatables.net/download/

Finally replace the file datagrid/DataTables/datatables.min.js with your downloaded file and set up the widget like this:

DataTables::create(array(
    ...
    "options" => array(
        ...
        "dom" => 'Bfrtip',
        "buttons" => [
            'copy', 'csv', 'excel', 'pdf', 'print'
        ],
    )
));

Please try this and let us know how it works for you. Thanks!