Sometimes you need 2 or 3 times more mandatory accessories for a main product. For example your main product smartphone requires 2 chargers instead of just one.
In this case you can use the following filter. Place that in your child theme functions.php. Then adjust the quantity and the accessory ID.
// Adjust mandatory quantity for accessory with ID 378 add_filter('woocommerce_product_accessories_mandatory_quantity', function($quantity, $accessory_id) { if($accessory_id == 378) { $quantity = $quantity * 2; } return $quantity; }, 20, 2);