adjust-quantity-input-values.php

/**
 * Adjust the quantity input values.
 */
function wb_woocommerce_quantity_input_args( $args, $product ) {
	if ( is_singular( 'product' ) ) {
		$args['input_value'] = 2;    // Starting value (we only want to affect product pages, not cart).
	}
	$args['max_value'] = 80;   // Maximum value.
	$args['min_value'] = 2;    // Minimum value.
	$args['step']      = 2;    // Quantity steps.
	return $args;
}
add_filter( 'woocommerce_quantity_input_args', 'wb_woocommerce_quantity_input_args', 10, 2 ); // Simple products.
/**
 * Adjust the quantity input values for variable product.
 */
function wb_woocommerce_available_variation( $args ) {
	$args['max_qty'] = 80;      // Maximum value (variations).
	$args['min_qty'] = 2;       // Minimum value (variations).
	return $args;
}
add_filter( 'woocommerce_available_variation', 'wb_woocommerce_available_variation' ); // Variations