"What if the umbilical cord has fallen off and your baby has an outie belly button? How can you make it an innie for the next baby?"
The belly button is really just a scar. If your baby had a hernia, this could have contributed to an outie belly button. Also, if your baby formed some scar tissue underneath the belly button, this could have caused it to protrude and become an outie.
While an outie belly button is less common, it's no less a part of your child's normal appearance. As your child grows, be sure to help your child see the beauty of this feature just like you would anything else that's a little different like freckles or a birthmark.
Source: New York Times, "Navel Perspective"