How can I lose this ?

I'm not naturally skinny but I'm not fat.i had a baby 1.5 years ago and I'm a member at the gym which I go every other day.i lost practically all my baby weight except for that bottom part of my stomach.it really doesn't stick out wit clothes on and all but of course I'm not happy with it when undressed. isn't the gym enough...I've been there almost a year and can't seem to tighten up my lower abs.any suggestions?
How can I lose this ?
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