Sleep training 6 year old?!

How do you get a 6 year old to sleep in their own bed? My bfs son wakes up about 3-5 times a night, barging into the room, swinging the door open like he’s the police! He doesn’t complain about bad dreams, being scared nor does he seem scared. He’s really calm and just wants to be walked back to his room. He has his own room here but at his moms house he shares a room AND bed with her so I think that’s definitely not helping the situation at all.

I’m due in about 3 weeks and I don’t want this to be a problem for the baby when the baby comes, as in him waking the baby up after the baby has just fallen asleep, startling the baby and making us more sleep deprived than we are already going to be. I understand babies wake up multiple times in the night, I know I need to be used to waking up a lot of times in the night w/ a newborn. But like I said, i don’t want the baby to be woken up/crying in the night more than he would usually. It’s just so frustrating, we literally wake up every other hour due to him barging into the room and I know it’s gunna be more frustrating when the baby comes.

We’ve asked why he comes in and he says it’s because he woke up. He literally just wants to be carried back to bed, he comes in the room pretty much still sleeping.