Hi Hozefa,
Thank you for your purchase.

You can do this by adding this code at very bottom of your theme function.php file

function landscapePDF ( $obj, $table_id ) {
   foreach ($obj->dataTableParams->buttons as $key => $value) {
      if (isset($value['orientation']) && $value['orientation'] == 'portrait') {
         $obj->dataTableParams->buttons[$key]['orientation'] = 'landscape';
      }
   }
   return $obj;
}
add_filter('wpdatatables_filter_table_description', 'landscapePDF', 10, 2);

If you do not now how to do this please take a look  at our Video tutorial

Best regards.