This is a filter removing specified frequency with use of FFT algorithm, enabling removal of specified frequency what you want. It is very useful in removing undesirable frequency component contained in signals.
Select data you want to apply this method in Analysis Window and click the icon of Notch FFT-Filtering in Analysis Tool Bar. This will display a dialogue box for frequency setting as shown in the below. Input frequency as you want and click Apply button. Then, you can get results from removal of the specified frequency in Display Window, which are registered at Analysis Window.