My Pspice manual is 15 years old, so the interface may be different, but somehow you have to get the SPICE command into the SPICE file. The command is: .AC XXX p f1 f2
Where XXX is either:
LIN for linear frequency scale
OCT for logrithmic scale by octave
DEC for logrithmic scale by decade
p is the number of data points per OCT or DEC
f1 is the start frequency
f2 is the end frequency
Note the period in front of AC, which denotes a command
The interface may be presented as a Fourier converter, but you will have to fill in the parameters.