How to edit the default comment title?

You can probably try somthing like this – untested…

add_filter('comment_form_defaults', 'wpse379939_comment_form_modification');
function wpse379939_comment_form_modification($defaults){

    // check if we have 2 or more comments..
    if ( get_comments_number() >= 2) {

        $defaults['title_reply'] = __('Add Your Voice To The Topic!');   

    }

    return $defaults;

}