First: You need tvOS 14.5 or higher and an iPhone with Face ID to do this.
Go to Settings → Video and Audio → Color Balance and start calibration.
Follow the instructions on the screen
Calibrate your Apple TV's color display
NEXT TIP
How to Customize the remote buttons on your Apple TV
Go to Settings → Remotes and Devices Click on TV button to make it show the Home Screen instead of opening the Apple TV App.
TIP FROM
8 Apple TV Tips and Settings
How to customize Apple TV remote, pair AirPods, calibrate display, and set up screensavers