If you have previously downloaded CC on TSR and placed in manually in your Mods folder, then it will unfortunately not show up. With the CC Manager you can only manage CC that has been installed using the 'Install with CC Manager' button on TSR.
Troubleshooting Can't see previously installed CC in the CC Manager This page is ment for providing help with any issues that can show up with the CC Manager. A short explanation and the download link can be found here:
The TSR CC Manager is a VIP membership only tool for easy downloading and installing Sims 4 and Sims 3 Custom Content (CC).