If you need to use Premiere Pro CS6, you will have to install from your Cloud account... do be aware that the software stops working if you do not pay each month
http://helpx.adobe.com/encore/kb/encore-cs6-installed-cc.html and do ALL of the steps
You may also buy a "forever" version of CS6 without the Cloud... just what do you want to do?
You should not have to reinstall. You can either enter the serial number if you bought CS6 outright, or sign into the Creative Cloud desktop app if you went that way.