Canon EOS-1D X Instruction Manual page 39

Selecting [Clear card's transf. history] will set the transfer history of
images on the memory card to "unsent." This enables you to resend all the
images on the card later by selecting [Card images not transferred].
Transfer the images.
5
Select [FTP transfer].

Select [OK] on the confirmation

screen displayed next.
 A transfer progress screen is
displayed.
Batch Transfer
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