Chronotherapy is a way to shift the sleep phases by going to bad a little later every day.
Shift does not have to be big. An hour or two is enough.
4-hour shift is too much and would induce unnecessary sleep deprivation.
Vice versa (going to bed earlier every day) does not usually work. You’ll just have harder times falling asleep.
I’ve done chronotherapy a couple of times and it worked great.
Controlled sleep deprivation with phase advance—another method of shifting sleep phases.