Canon EOS-1D X Mark III Advanced User's Manual page 490

3.
Select the image to be rated.
Turn the <
4.
Rate the image.
Press <
screen shown above.
Turn the <
When you append a rating mark to the image, the number beside the
set rating will increase by one.
To rate another image, repeat steps 3 and 4.
Note
By pressing the <
> dial to select the image to be rated.
>, and a blue highlight frame will appear as shown in the
> dial to select a rating mark, then press <
/ > button, you can also rate images during playback (
490
>.
).