How can I tone up my belly?

I'm 5'4 and 79 pounds and I need to tone up my belly because it isn't exactly toned lol so what exercises can I do?
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I'm naturally 79 lbs what am I suppose to do?My doctor knows of my weight and says I am healthy.My hair is long,skin clear and I still get my period.If you're going to be an ass to me I will block you
How can I tone up my belly?
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