I used to stay up until around 1am every night. I found it very easy to fix this - I now go to the gym at 5:30am. Within a couple of weeks I found it very easy to go to sleep at 10pm or earlier. It’s more than just getting up early - you’re telling your body you need it to be ready to perform early in the morning. Just like a muscle grows when you demand more of it, I think this sets off an adaptive reaction that results in earlier and easier sleep.