If you use iOS 12 or newer, do this:
Step 1: Open Settings.
Step 2: Click on Screen Time.
Step 3: If you haven’t set it up already, then set it up for yourself.
Step 4: Click Downtime.
Step 5: Click the toggle next to Scheduled.
Step 6: Customize the times. Preferably, have the start time be your bedtime (or earlier) and have the end time be your wake-up time (or later).