Canon EOS REBEL T8i Advanced User's Manual page 340

4.
Set the shutter speed and aperture value.
Press the shutter button halfway and check the exposure level
indicator.
To set the shutter speed (1), turn the <
aperture value (2), turn the <
5.
Focus and record the movie.
The procedure is the same as steps 3 and 4 for
Recording.
> dial.
340
> dial, and to set the
Autoexposure Movie