When updated user role user get a notification email. This solution using php and html . 

#wp_mail() #user_role_update

// Role Update Notification [action on the page of user edit/update]
function user_role_update( $user_id, $new_role ) {
    $site_url = get_bloginfo('wpurl');
    $user_info = get_userdata( $user_id );
    $to = $user_info->user_email; 
    $subject = "Laderach B2B catalogue account active ";
    $headers = array('Content-Type: text/html; charset=UTF-8');
    $message = "Dear " .$user_info->display_name . "
 Hello Customer Your Role has been updated please login and check your account status.
Please login at ".$site_url."/login"."
Thank you";
    wp_mail($to, $subject, $message, $headers);
}
add_action( 'set_user_role', 'user_role_update', 10, 2);