functions.php

// remove a column
function wc_csv_export_remove_column( $column_headers ) {

    // the list of column keys can be found in class-wc-customer-order-csv-export-generator.php
    unset( $column_headers['coupon_items'] );
 
    return $column_headers;
}
add_filter( 'wc_customer_order_csv_export_order_headers', 'wc_csv_export_remove_column' );