Canon EOS-1D X Mark III Advanced User's Manual page 538

Sending images individually
1.
Select an image to send.
2.
Select [Send img shown].
Sending multiple selected images
1.
Press <
Turn the < > dial to select an image to send, then press <
You can press the <
counterclockwise to select the image using the index display.
In [Size to send], you can select the image sending size.
>.
> button and turn the <
538
>.
> dial