@susanp7777 you can use bellow code to add functions.php. But I don’t recommend to do like this follow up @stephencottontail reason.
function wimple_remove_allowed_tags_text() {
add_filter('comment_form_defaults','wimple_comments_form_defaults');
}
add_action('after_setup_theme','wimple_remove_allowed_tags_text');
function wimple_comments_form_defaults($default) {
unset($default['comment_notes_after']);
return $default;
}