set up of discover dipole moment autocorrelation function

I can't figure out the sets to use for the dipole moment autocorrelation function. What type of sets should be used? When I have a molecule as a set, it does not appear in the set drop down. We have the trajectory file, and we have also tried separating the .his and .car files. Our version of MS is old, 4.2, but any help is appreciated.