Canon Speedlite 430EXIII-RT Instruction Manual page 44

Flash Control from the Camera's Menu Screen
Flash Custom Function Settings
You can set Custom Functions for the Speedlite from the camera's
menu screen. The details displayed vary by the camera. If C.Fn-21 to
23 are not displayed, set them by operating the Speedlite. For the
Custom Functions, see pages 83-85.
Custom Function number
When using a camera released in 2011 or earlier, or EOS REBEL T5/
1200D, the C.Fn-21 to 23 settings are not cleared even if [Clear all
Speedlite C.Fn's] or [Clear ext. flash C.Fn set.] is selected. When the
procedure described in "Clearing All the Custom/Personal Functions" on
page 82 is performed, all the Custom Functions (except C.Fn-00) are
cleared.
Personal Functions (P.Fn/p.86) cannot be set or all cleared at once from
the camera's menu screen. Set them by operating the Speedlite.
44
Select [Flash C.Fn settings].
1
Select [Flash C.Fn settings] or
[External flash C.Fn setting].
The flash Custom Function settings
screen is displayed.
Set the Custom Function.
2
Select the Custom Function number,
then set the function.
To clear all the Custom Function
settings, select ([Clear settings],)
[Clear all Speedlite C.Fn's] or [Clear
ext. flash C.Fn set.] in step 1.