Add labels to WooCommerce Product price

wc-product-price-display.php

<?php
// only copy opening php tag if needed
// Adds "per package" after each product price throughout the shop
function sv_change_product_price_display( $price ) {
	$price .= ' per package';
	return $price;
}
add_filter( 'woocommerce_get_price_html', 'sv_change_product_price_display' );
add_filter( 'woocommerce_cart_item_price', 'sv_change_product_price_display' );

Hi, can i ask you where to add this code, i try to figure out with the editor, dont find wc-product-price-display.php file.
I suppose i have to create it and add it inside the woocommerce plugin folders? Or i have to edit an existing files?

Can you explain, where to put this?