You can curve the edge of a fill using the Curve tool. Once the tool is active, you can click and drag the edge to curve it, or select a point to curve to.
To curve a fill edge by clicking and dragging:
Click on the fill edge that you want to curve.
Right-click and select Curve, or select Edit > Modify Elements > Curve.
Click and drag the fill edge to the desired curve.
Release your mouse button.
To curve a fill edge to a selected point:
Click on the fill edge you want to curve.
Right-click and select Curve, or select Edit > Modify Elements > Curve.
Select the point you want to curve to. The fill edge automatically curves to the point.
Click to finish.