How to call a funcion via a dropdown or a input? (Woocommerce funcion)

Question

This is the function I want to call

function test() {
echo "test";
add_filter('loop_shop_per_page', create_function('$cols', 'return 24;'));
}

And I call it like this

<?php test() ?> 

So it shows me the "test" text but not make the "filter"

To be more specific, I want to show a dropdown with this options :10, 20, 30 so I can sort the list of products on a woocommerce site.