Canon EOS-1D X Mark III Advanced User's Manual page 477

2.
Select an item, then select images.
You can select multiple images to process at once.
Selecting images
Turn the <
Press the <
Selecting range
Select the first image (start point).
Next, select the last image (end point).
Press the <
To process other images, repeat this step.
> dial to select images to process, then press <
> button.
> button.
477
>.