M.C.
What I would recommend is putting a potty chair in his room. When he asks to be changed, do the routine you did when you were day training him - put him on it even though he already went and explain this is where we go potty even at night. Eventually he will understand that instead of going in his diaper, he can get up and use the potty. Or you can take him to the bathroom and do the same, either way. But it's definitely time to start night training. His body may not be ready to wake him up to go potty but this is the way to start initiating the process. It may take him a while to get it and I would say keep him in diapers for a while until he starts waking up dry asking to use the toilet otherwise you will be cleaning a lot of wet bedding.