Use Q-tips dipped in your usual body wash/ bath soap , gently cleanse inside the "belyrics button. You'll use as many Q-tip swabs as needed , # depends on how much dirt, oil , lint , debris,etc.you have there.
After cleaning use alcohol on new swabs inside the bellybutton. This will also help to dry out the belly button.
Clean your bellybutton every time you bath or shower.