My son's friend gouged an indention into the plastic covering over the screen on the Wii U controller
I was able to completely disassemble the Wii U controller pad all the way down to the screen, however, the plastic screen overlay is not removable, so I was unable to complete the repair. The whole screen assembly, plastic guard included, has to be replaced.
The ribbon cables in the Zif sockets have to be removed carefully. All the little zif sockets have flaps which open up to allow the cable to be removed. Brute force might work too, but may damage the cable, or may break the socket itself.