Canon EOS-1D X Manual (en)

Click the [
] button.
The [Add or Remove lens data] window appears.
To use this function, an environment with Internet access 
(subscription to a provider, browser software installed and an in-
place line connection) is required.
An administrator-level privilege is required for this operation.
Before you click the [
] button in step 2, Lens data [No] may 
be displayed instead of [Not Available] for non-compatible images.
Checkmark the checkbox for the lens used to shoot 
the image, and click the [Start] button.
The lens data is downloaded to your computer. 
When the downloading of the lens data ends, the indication for 
the lens data changes to [Yes].
You can download the data for up to 30 lenses at the same time. 
If you remove the check mark from the checkbox for already-
downloaded lens names and click the [Start] button, the lens data 
will be deleted from your computer.
Depending on the type, current state, etc. of software running on 
your computer, the download of the lens data may fail. If it occurs, 
wait for a while then try downloading the data again.