It's not there.
The 13.1.2 update is only for Creative Cloud users (which is an issue all its own).
I tried deactivating from Help->Deactivate, and then Help->Updates and it lets me update to 13.1.2 but the update fails to install! (Others have reported this.)
There is something called the Creative Cloud Cleaner Tool
http://www.adobe.com/support/contact/cscleanertool.html
but it sounds too scarey to use.
And I wonder what happens if I cancel my Creative Cloud subscription at some point (I signed on with a subscription so I could use InDesign, Premiere Pro, and Illustrator on a new project) ... if I cancel, do I then lose access to Photoshop, even tho I paid for a real license??
I can find no information on this possible conflict between licenses on the Adobe website. Nor can I find a phone number to call support. Sheesh!