EOS 5D Mark IV: Auto ISO

The EOS 5D Mark IV allows you to set the ISO to Auto, while the shutter speed and aperture are set manually. This allows you to keep the particular shutter speed and aperture you require while allowing the ISO to adjust to achieve the correct exposure. In this setting, exposure compensation can also be used to adjust the standard metered exposure. If you find the exposure compensation seems to have no effect, this is likely because you are using flash. With flash, even if exposure compensation is set, it will have no effect.
Camera settings
EOS 5D Mark IV