From Canon USA:
Changes:
Firmware Version 1.0.2 incorporates the following functional improvements and fixes.
The Version 1.0.2 firmware being released at this time is for cameras with Firmware Version 1.0.0. If the camera's firmware is already Version 1.0.2, it is not necessary to update the firmware. When updating the firmware of your camera, please first go over the instructions thoroughly before you download the firmware. The firmware update takes approximately six minutes.
Download: Canon EOS-1D X Mark II Firmware v.1.02