Canonical URL search page

Hi. I have search page Anunciospty.com
If select city , canonical redirect to default search page. Any solutions ?
anunciospty.com/buscar
Anunciospty.com/buscar/city_122example , canonical tag point to another page - default search page. Tks

In osclass core functions.php find
function osc_generate_canonical() {
  if(osc_always_generate_canonical_enabled()) {
    $url = osc_apply_filter('canonical_url', osc_get_current_url());
    View::newInstance()->_exportVariableToView('canonical', $url);
  }
}
Replace with:
function osc_generate_canonical() {
  if(osc_always_generate_canonical_enabled() && !osc_is_search_page()) {
    $url = osc_apply_filter('canonical_url', osc_get_current_url());
    View::newInstance()->_exportVariableToView('canonical', $url);
  }
}
basically it's overwritten that's the reason.

I have this :
// Generate canonical URL on all pages
function osc_generate_canonical() {
  if(osc_always_generate_canonical_enabled()) {
    $url = osc_apply_filter('canonical_url', osc_get_current_url());
    View::newInstance()->_exportVariableToView('canonical', $url);
  }
}

osc_add_hook('init', 'osc_generate_canonical', 1);

done. tks.

It is better to modify the functions.php file using a child theme to prevent losing changes when the theme is updated in the future. 

Mostly yes.
But even best is to create elemental plugin with just index.php that does not exists where you can put your custom functions