Add PO Number to Customers > Orders

// Display purchase order number in a new column on Woocommerce "My account" page orders table

add_filter( 'woocommerce_my_account_my_orders_columns', 'mwd_product_column', 10, 1 );
function mwd_product_column( $columns ) {
    $new_columns = [];

    foreach ( $columns as $key => $wc_purchase_order_number ) {
        $new_columns[ $key ] = $wc_purchase_order_number;

        if ( 'order-status' === $key ) {
            $new_columns['order-items'] = __( 'PO Number', 'woocommerce' );
        }
    }
    return $new_columns;
}