Your answer is in this link: http://www.mathworks.com/help/dsp/ug/use-fdatool-with-dsp-system-toolbox-software.html#f3-21562
Select Notching from the Differentiator list in Response Type. Select IIR in Filter Design Method and choose Single Notch from the list. For the Frequency Specifications, set Units to Hz and Fs, the full scale frequency, to 1000. Set the location of the center of the notch, in either normalized frequency or Hz. For the notch center at 440 Hz, enter 440. To shape the notch, enter the bandwidth, bw, to be 40. Leave the Magnitude Specification in dB (the default) and leave Apass as 1. Click Design Filter. FDATool computes the filter coefficients and plots the filter magnitude response in the analysis area for you to review.
