add_filter( 'tablepress_export_data', 'tablepress_add_bom_to_csv_exports', 10, 4 );
function tablepress_add_bom_to_csv_exports( $export_data, $table, $export_format, $csv_delimiter ) {
  if ( 'csv' === $export_format ) {
    $export_data = "\xEF\xBB\xBF" . $export_data;
  }
  return $export_data;
}