In Shapes, choose the arrow shape, with it highlighted go to Format>Shapes>Make Editable, There should be 2 red dots at either end of the arrow now, click on one of the dots and it should change to a white dot outlined in red, go back to Format>Shapes>Smooth Path and that will add a third dot on the arrow that you can now manipulate.
I know this is a long process but I just taught myself how to do it researching for you...