Melatonin. It’s an herbal supplement. Take it half an hour to an hour before you’d like to go to sleep. You’ll be out.
I have delayed sleep phase syndrome (can only sleep from like 4-5am on) and i’ve been taking it ever since i got a full-time day job. Hasn’t failed me yet. When I tried not taking it one night, sure enough, couldn’t get to sleep before 4:30 for an 8AM wakeup.