You install the same way you did the 1st time... put your disc in the drive and enter your serial number when asked, or download the installer and enter your serial number when asked
kglad links in reply #1 here https://forums.adobe.com/thread/2478335 to download program installers
Which does not mean that you will actually be able to install that old version on your new operating system
CS6 and earlier programs have not been tested and will not be updated for Mac El Capitan or later operating systems
-which means that you try to use CS6 and earlier at YOUR risk of having problems due to Apple updates
-Apple did not maintain backward compatibility with old programs in El Capitan or Sierra
--Adobe has a workaround to Apple's problem of not maintaining backward compatibility
--READ HERE https://forums.adobe.com/thread/2301916 for an Adobe solution to installing old programs, including a link to installing the old Java runtime that is required
--Also read for more information https://forums.adobe.com/thread/2458382