Adding custom field in woocommerce from a theme directory

Hi there!

I'd like to insert a new field in the user profile in the backend, like another phone number or a website url. The easiest way is to edit directly the class-ac-admin-profile.php file. But a Woocommerce update will overwrite the code. So I'd like to insert this line using my theme directory.

public function get_customer_meta_fields() {
		$show_fields = apply_filters('woocommerce_customer_meta_fields', array(
			'billing' => array(
				'title' => __( 'Customer Billing Address', 'woocommerce' ),
				'fields' => array(
					'billing_phone' => array(
						'label'       => __( 'Phone Number', 'woocommerce' ),
						'description' => ''
					)
				)
			)
		) );
		return $show_fields;
	}

Thank you.

Marc