Some people have reported that taking 0.3mg melatonin five hours before desired bed time was helpful. Sort of imperfectly turned me from a 6AM-1PM sleep schedule to a 1AM-9AM, sometimes better, and when I stopped after a few months it was easier to stay closer to diurnal. But blue light filters (f.lux etc.), dimmable lights, and timed lighting were also necessary, and nothing is 100% sufficient.