How to add Placeholder for Registration fields?

I find this examle for acount placeholder. and try to macke the same. But it dosen’t work.

function um_add_placeholders_to_registration_fields($args) {
    if ($args['form_id'] === 'register') {
        $args['fields']['first_name']['placeholder'] = 'First Name';
        $args['fields']['last_name']['placeholder'] = 'Last Name';
        $args['fields']['user_email']['placeholder'] = 'Email';
        $args['fields']['user_password']['placeholder'] = 'Password';
        $args['fields']['user_password_confirmed']['placeholder'] = 'Confirmed Password';
    }
    return $args;
}
add_filter('um_add_register_fields', 'um_add_placeholders_to_registration_fields', 10, 1);