Canon EOS-1D X Mark III Advanced User's Manual page 130

2.
Select a custom white balance number to be registered.
Press <
Turn the <
press <
selected number.
3.
Select [Record and register WB].
The screen now turns off, and the selected number blinks on the top
LCD panel.
>.
> dial to select a number from 1 to 5 for <
>. The custom white balance will be registered to the
130
*>, then