Night Shift automatically adjusts the colors of your display to the warmer end of the spectrum — making the display easier on your eyes. Night Shift uses the clock and geolocation of your device to determine when it’s sunset in your location. Then it automatically shifts the colors of your display to warmer colors. In the morning, it returns the display to its regular settings. There are two ways of enabling Night Shift - either through Control Center or through the Settings.
How to enable Night Shift through Control Center
Open Control Center
Firmly press the Brightness control icon
Tap the sun/moon icon to turn Night Shift on or off
How to enable Night Shift through Settings
Go to Settings > Display & Brightness > Night Shift
Schedule a time for Night Shift to turn on automatically, then adjust the color temperature
If you don't schedule a specific time frame for Night Mode, by default, it will turn on from sunset to sunrise.