I had this problem. Just recently fixed it.
Here's what I did:>stayed up around 4 hours later than normal>woke up 4 hours later>stayed up a further 4 hours later>woke up a further 4 hours later>kept doing this every day until I ended up waking at desired time>religiously go to bed at same time and always wake up at consistent time- this is the hardest part in the long run
Pro tips:>don't try to stay up way later than usual, like 12 hours
Your body will fuck with you if you do that.>if you wake up too early address the problem immediately
With a sleep schedule you're trying to fix your body is going to be out of wack and might be producing too much urine when you're asleep, so you might have to pee and that's what's waking you up even if while you're laying in bed you don't feel like you have to pee. Could also be you're too hot or cold. Or you ate too close to going to bed, try to leave at least three hours between eating and sleeping.