Mine has never had it, but it sounds like it is obvious. I squeeze the under side of mine just a little every once in a while just to be sure all is fine. I don't think you have to really squeeze much at all if it were soft. Hope that helps
Newborns shells arnt to hard to begin with, if you sqeeze it and cannot notice anything you are fine!
you want to worry when his shell is hard and gets very soft
Tortoises normally have soft shells when at a young age. But when it grows bigger, their shell should be harder by then. Make sure to give it enough calcium to make its bones strong and healthy.
My hermann's was rescued from craigslist with severe mbd, and she felt like a hacky sac. It was very noticeable and her shell was very deformed (divoted in the back and kind of melty looking and flat around the edges). She slowly "stiffened" with calcium injections, lots of water, and UV and she feels pretty much normal now, but her shell is still a funny shape (less noticeably so as she grows).