Actually the addon domain does not have a Customer Area due to the fact that it's not an independent account, but it's just an additional feature to your current account. In order to be able to manage your addon domain, you'll have to login into your cPanel, then click on Addon domains. There you'll be able to manage and point your addon domain name to the exact directory that you want.
cPanel is easy to work with when you have the right host to support you. If you need a reliable partner to help you manage your website with cPanel, check out our cPanel hosting services!