Canon EOS-1 D X Mark II Instruction Manual page 93

Selecting the AF Area Selection Mode
With [24: Select AF area selec. mode], you can limit the selectable
AF area selection modes to only those you want to use (p.131).
If you set [24: AF area selection method] to [S9Main Dial], you
can select the AF area selection mode by pressing the <S> button,
then turning the <6> dial (p.132).
S Selecting the AF Area and AF Point
Press the <S> button
1
Press the <B> button.
2
Look through the viewfinder and
press the <B> button.
Each time you press the <B>
button, the AF area selection mode
changes.
.
(9)
93