Your belly didn't get soft in one week and it certainly won't get flat in 1 week. The fastest way to achieve results is through a regular exercise program and a balanced diet with slightly restricted calories.
Any good moderate to vigorous exercise done daily, around 20 to 60 minutes a day, with a low carb diet will help reduce your fat all over, including your abs. Click below for how we do our diet program. Doing 300 crunches a day can really help strengthen an bulk the abdominal muscles too. Good luck.