Answer:
And the LORD God formed man of the dust of the ground . . . and man became a living being . . . . Then the rib which the LORD God had taken from man He made into a woman (Genesis 2:7, 22).
You are not the first one to wonder about Adam’s bellybutton! Do you know that our bellybuttons are scars left over from when we were born? When a baby is growing in her mommy’s tummy, she needs food. She gets food through a cord attached to her mommy. We all needed that cord in order to survive and grow! Our bellybuttons are scars from the cord that once fed us. The Bible tells us that our great God made the first man (Adam) directly out of dust. He was already an adult, so he didn’t need a cord to get food.
The Bible also tells us that God made the first woman (Eve) directly from the rib of the man. So she was an adult too. I think it is very possible they did not have or need bellybuttons.
Source: https://answersingenesis.org/kids/adam-and-eve/did-adam-and-eve-have-bellybuttons/