From Canon USA:
Firmware Version 1.0.4 is incorporated with the following correction.
Firmware Version 1.0.4 is for lenses with Firmware Version 1.0.3 or earlier.
Lenses whose third digit in the serial number is "0". (xx0xxxxxxx)
If the lens' firmware is already Version 1.0.4, it is not necessary to update the firmware. The lens firmware can be checked through the menu on the EOS 5D Mark IV.
Preparations for the Firmware Update:
In the folder you downloaded are the firmware (file name: EF012104.lfu / file size: 1,441,844 bytes), and instructions on the firmware update procedures (a PDF file in five languages: Japanese, English, French, Spanish, and Simplified Chinese).
Before starting the firmware update operations, please be sure to carefully confirm your understanding of these instructions.
Download: Canon EF 24-105mm f/4L IS II USM Firmware Version 1.0.4