These are just the few things I have picked up from experience on how to control my body clock, with tricks like this I have managed to wake up functionally at 6am most mornings.
1) Routine
You need to always wake up early, not just on weekdays or you will begin to slip back into your old ways. If you can keep it up, your sleep cycle will begin to get set as a morning person, because I have to get up so stupidly early for work each morning, even on weekends I usually wake up only an hour or two later than I would for work.
2) Control your bedtime
I find, as a night owl myself, it is easier to shift your sleep cycle later than earlier so staying up late is a big no, or you will easily shift back to night owl.
3) Control light exposure
Have thin curtains so the morning light helps wake you up, and try to keep your lights dimmer and more orange (less blue light) later at night before bed, your body-clock works a lot from light cues from day and night cycle, show it when to be awake and asleep with the light
4) Don't have TOO comfortable a bed
I found in my 3rd year of University I had great trouble waking up in the mornings which shifted me more and more towards night owl, in the end I swapped my mattress for a harder one and I found it much easier to wake up (my old mattress was just TOO comfortable) In fact, if I just want to sleep an hour or so, I sometimes just sleep on the floor with a pillow, after an hour my body just says "Ok, that's enough of that" and wakes me up naturally.
5) Have a purpose to getting up every morning
Dont just get up for the sake of it every morning, have a damned good reason to be up at that time every morning, I find that if I decide "Ok, i want to be awake at xx:xx in the morning", without an alarm, thats just wishful thinking, but if its important like going to work or an important deadline, and I NEED to be up, I will wake up on my own, often before my alarm. If you can come up with a terribly compelling thing you need to be awake for every morning, something vital, this will help you wake up naturally.
6) Bed is for sleep
Dont use your bed for anything but sleep, no playing with phones before sleep, no lay-ins, when in bed, go straight to sleep, when you wake up, GET up as soon as you can, that way your mind will build up a stronger association between bed and sleep, giving you better sleep and helping you control your sleep cycle easier.
Of course I dont follow all of these, but I do pull them out when I need to, and follow several of them religiously, and just as a bonus, one extra:
x) Early Worm is just EXTREME Night Owl.
As a night owl, I find if I just go to sleep when Im tired and wake up when I'm happy, I will drift by an hour or two every day, more than once, I turn fully nocturnal and end up deciding that the easiest way to fix it is just to keep going, waking up as late as possible each day, staying up as late as possible each night, getting later and later until I wake up so late I have cycled right around to being a morning person again.