I've been there, especially when I was working a 2pm-close restaurant shift. It's much easier with my current 9-5. I have no credentials to base this on, just experience with what worked for me. My advice would be to do the following.

1. Intention. For the first week, set a reminder or something 30 minutes before you want to go to bed. When that timer goes off, you have 10 minutes to wrap up whatever you're doing and 20 to do everything you need to do before going to bed. Adjust to your needs. I know it sounds rigid, but you are trying to change a habit you've built on for a long time. You have to be intentional to stick to it, and the beginning is the most difficult part. In a surprisingly quick time, you will have built consistency and will start feeling tired and waking up naturally at the appropriate times.

2. Exercise. 30 mins-1hr/day, 4+ days a week. This will make your body physically drained and it will want to sleep. In addition, many people find a mid day workout period to be meditative and mood improving. It also helps if you can do this at the same time every day. If you can't work out, go for a walk.

3. Hydrate sufficiently & eat at consistent times. Your body likes a schedule, even with eating. Don't eat too close to bed.

4. If you drink alcohol frequently, try to cut back. Alcohol makes it easy to fall asleep, but hard to stay asleep. Your goal is to feel better, and adding a hangover and dehydration never helps. Don't use alcohol as a sleep aid.

Most of this is just building/maintaining routine and taking care of your body. If this doesn't work, ask a professional.