Canon EOS-1D X Mark III Advanced User's Manual page 407

Focus guide
Setting [Focus guide] to [On] in Live View shooting provides a guide frame that shows
which direction to adjust focus and the extent of adjustment needed. The guide frame is
displayed near any eyes that are detected for the main subject when [
set to [ +Tracking] and [
1.
Select [
2.
Select [On].
: Eye Detection AF] is set to [Enable].
: Focus guide].
You can use < > to move the guide frame in the direction you press.
You can also tap the screen to move the guide frame.
To return the guide frame to the center of the screen, press <
straight in or press the < > or < > button.
407
: AF method] is
>