How to fix kitchen unit that's out of square?

One of our kitchen units appears to be out of square. The bottom face of the drawer does not sit flush with the surrounding units and juts out by approximately 5mm. I have come to the conclusion that it is the actual unit that is causing this. The kitchen is from IKEA so we replaced the drawer itself including the runners in case it was an issue with that. I have also made all the small adjustments that can be made to the drawer front to align it which hasn't helped. Is there a way of fixing this without having to resort to removing the whole unit? We have quartz worktops so it wouldn't really be practical to do so.