First we are going to get the pie chart out of our way without deleting the object from the sheet.
Right-click on the pie chart and bring up its Properties. Navigate to the Caption tab on the right. You may need to use the left < > right arrows to see it.
Under the Caption tab, you will see the Allow Minimize and Allow Maximize checkboxes on the bottom-right corner. Check them both, click Apply, and close the wizard. Now you will see the standard computer display symbols for minimizing a window.