The code you're looking for would actually be in the /components/com_jfbconnect/models/loginregister.php file. Around line 295, you'll see:
$defaultUserGroup = $config->get('new_usertype', 2);
$instance->set('usertype', 'deprecated');
$instance->set('groups', array($defaultUserGroup));You'd want to update that last line with whatever group the user should be in. You can find the group IDs in the User Manager of Joomla. Use the IDs there in that last line. So, if the user should be in group 5 and 10, you'd update it like:
$instance->set('groups', array('5', '10'));Test that and let me know how it goes.
Thanks,
Alex