How can I change the wording on the circle noting that a product is out of stock and can be backordered from "Available for Backorder" to "Special Order"?

I tried adding this to my functions.php, but saw no different results:

function backorder_text($availability) {

foreach($availability as $i) {

//$availability = str_replace('Available for backorder', 'Desired Text', $availability);
 
$availability = str_replace('Available for backorder', 'Special Order!', $availability);
 
}
 
return $availability;
}
add_filter('woocommerce_get_availability', 'backorder_text');