See more related video:Quick Fit Gadget Tutorial
The Quick Fit tool allows you to select a region of interest on a graph and then perform curve fitting on the region. You can choose to fit with one of the functions in the function list. The list is editable, so you can add any built-in or user-defined function to it.
To use the tool, make sure that the graph containing the curve is active, and then select Gadget: Quick Fit: the desired function from the Origin menu.
For more details on the tool, please read the Quick Fit page in the Regression and Curve Fitting chapter.