First off, you should do some exercise. That will help tire you out, and put you into a deeper sleep, for longer.
Day 1 to Day 3: Take melatonin pill at 11:30 PM, get in bed. No screens. If you want, you can masturbate to help you sleep, but after that, absolutely no screens at all. (yes I am serious)
Set an alarm for 3 AM, and even if you do wake up before that, do NOT get out of bed. After 3, if you still feel tired, then sleep. If not, then take one pill at 8 AM and set an alarm for 2 PM. You MUST get up at this time. Repeat this for FOUR more days. You will do this for five days in total.
Day 4 to Day 8: Take a melatonin pill at 11:00 PM, get in bed. Same as the last few days, no screens, jack off if you want. Set an alarm for 5 AM. If you feel sleepy, continue to sleep. If not, then get up. Take a pill at 9 AM and set an alarm for 2 PM. Get up.
Day 9 to Day 12: Pill at 11 PM, set alarm for 6AM. Sleep if you want. Pill at 10 AM, alarm at noon. Get up.
Day 13 to day 15: Pill at 11 PM, set alarm for 7 AM. Sleep if you want. Pill at 10 AM, alarm at noon. Get up.
After the fifteenth day, follow this until your sleep schedule is fixed: Pill at 10:30 PM, and do not get up until atleast 8 AM. No afternoon naps, only one big sleep.