Enabling Spam Assassin in cPanel :
1. Login to the Cpanel with your username and password
2. Click on Mail > Spam Assassin
3. You will see the status indicating that Spam Assassin is : disabled. To enable the Spam Assassin for your domain, click on the "Enable Spam Assassin" button at bottom of the page.
4. The installation will proceed and once done, you will be prompted for a message that Spam Assassin has been enabled for your domain.
Note: You might not able to find SpamAssassin from your cPanel for some case as Xsosys had disabled user control SpamAssassin, however it was enabled from server wide.