How do I implement sorting?

Here is an example of how you can implement sorting in your theme/search:

add_filter('elasticsearch_searcher_query', function($query){
    if(!isset($_GET['sort']) || $_GET['sort'] == 'date'){
        $query->addSort(array('post_date' => array('order' => 'desc')));
    }else{
        $query->addSort(array('_score' => array('order' => 'desc')));
    }
});