Reshape Paths by Drawing

Use the Pencil tool (N) to reshape any existing path by drawing. Make sure the path is selected, then click-and-drag with the Pencil tool to redraw the path. You must start fairly close to the path for Illustrator to recognize that you are redrawing versus creating a new path. How close? That depends on the preference for the Pencil tool. Double-click on the Pencil tool in the Toolbox to set the distance from the path in the Options section of the dialog just click Edit Selected Paths and choose your pixel amount.