Add entries from a collection into a dropdown for the navigation

I have a collection containing services, I would like to get these services items into a dropdown for the parent page. Can I somehow pass them into the navigation template by setting a variable?

What I can't get my head around it how I could pull out the titles with the corrosponding slugs for it to work as a dropdown. Or am I going about this all wrong, I just don't know. Advice or help appreciated.

As far as I've got:

$service_items = perch_collection('Services', [
    'template' =>'services.html',
    'skip-template' => true
]);

// main navigation
PerchSystem::set_var('service_list', $service_items);

Though I get Array to string conversion in, I am guessing because I am just grabbing everything, would I need to loop through each and do something?