custom redirect for signed up users

I use BuddyPress Autologin On Activation plugin to automatically confirm and log in new users. It redirects me to user profile page but what I would like to have it to be redirected to user profile page and add "?activated" at the end of the URL.
Can you let me know how to modify it, please?
I would preferable use bp-custom.php file.
You can find a source code of the plugin at

Kind regards,