Dropdown Select Post Filter

You can use tax_query for Taxonomy Parameters for your WP_Query.

$term_id = $_REQUEST ['soins-taxonomy'];  // or use $_POST or $_GET as the case may be

$args = array(
    'order' => 'ASC',
    'post_type' =>  'etablissements',


    'tax_query' => array(
        array(
            'taxonomy' => 'location',
            'field'    => 'term_id',
            'terms'    => $term_id,
      ),


    'posts_per_page' => 9,
    'paged' => $ourCurrentPage
);

I hope this may help.