add multiple search terms (custom fields)

Hello,

Thanks to this snippet I’ve added 1 custom field _my_meta_field to var $searchable_meta_keys.
How do I add a second or more custom fields to the search terms?
Perhaps only just a matter of proper php coding, nevertheless I feel stranded.
Perhaps anyone could point me out.
Thank you

function my_wpjm_meta_key_dm() {
    global $wpdb, $job_manager_keyword;
    $searchable_meta_keys[] = '_my_meta_field';
    return $searchable_meta_keys;
}
add_filter('job_listing_searchable_meta_keys', 'my_wpjm_meta_key_dm');