Assign an imported WordPress site to Softaculous so we can use the backup feature. 

Log into your cPanel
Select Softaculous Apps Installer under Software
Select WordPress from the list of popular installs (also under Blogs category)
Click Import in the Top Tabs on the WordPress page
Fill in the protocol, domain, and directory where the site resides (I usually visit the site and find out if its http or https and also www or non-www for the protocol.) 
Click Import button and you should be all set!