Canon EOS R6 Mark II Mirrorless Camera with 24-105mm f/4-7.1 Lens - Manual (Page 610)

3.
Change the orientation information.
As you watch the camera and icon in the upper left of the screen,
press the < > button to specify which side is up. Each press of the
< > button edits the movie rotation information as follows: [ ] →
[ ] → [ ].
Caution
Movies are played horizontally on the camera and via HDMI video output,
regardless of the [ :
Add rotate info ] setting ( ).
Movie orientation information of movies recorded with other cameras cannot be
edited with this camera.
610