functions.php

// Adjust Date Column Output
function wc_csv_export_format_data( $order_data ) {

    for( $i = 0; $i < count( $order_data ); $i++ ) {
        if ( isset( $order_data[ $i ]['order_date'] ) ) {
            $order_data[ $i ]['order_date'] = date_i18n( 'd/m/Y', strtotime( $order_data[ $i ]['order_date'] ) );
        }
    }

    return $order_data;
}
add_filter( 'wc_customer_order_csv_export_order_row', 'wc_csv_export_format_data' );