How am I supposed to get a flat stomach without being underweight?

I’m 5″4 and 112lbs.
I have a little stomach pouch (if you see what I mean) and I don’t understand how I’m supposed to get rid of it.
I mean, I could lose another 10lbs and be clinically underweight and it would be gone, but I can’t really do that obviously.

How do I get a fat free stomach?
I mean wash-board, as my tummy is already reasonably flat, it’s just the little pouch that gets me!

Thanks.