Use this snippet to override the initial quantity value of a bundled item (by default equal to the minimum quantity).

woocommerce-bundles-override-default-quantity.php

<?php
/**
 * Plugin Name: WooCommerce Product Bundles - Default Bundled Item Quantity Override
 * Plugin URI: https://woocommerce.com/products/composite-products/
 * Description: Use this snippet to override the initial quantity value of a bundled item (by default equal to the minimum quantity).
 * Version: 1.0
 * Author: SomewhereWarm
 * Author URI: https://somewherewarm.gr/
 * Developer: Manos Psychogyiopoulos
 *
 * Requires at least: 3.8
 * Tested up to: 5.3
 *
 * Copyright: © 2017-2020 SomewhereWarm SMPC ([email protected]).
 * License: GNU General Public License v3.0
 * License URI: http://www.gnu.org/licenses/gpl-3.0.html
 */
 
// To use this snippet, download this file into your plugins directory and activate it, or copy the code under this line into the functions.php file of your (child) theme.
// Note: Here, a product bundle id = 1000 and a bundled item id = 500 are assumed. Replace these with your own values!
 
add_filter( 'woocommerce_bundled_product_quantity', 'wc_pb_default_product_quantity', 10, 4 );

function wc_pb_default_product_quantity( $default_qty, $min_qty, $max_qty, $bundled_item ) {
	if ( intval( $bundled_item->get_id() ) === 500 ) {
		$default_qty = 1;
	}
	return $default_qty;
}

I also have done this, making the three necessary changes - and it doesn't work for me. Theme used is Bento.

Any ideas anybody?!

Chris