As I know that PMDG737 can tune the radio to the airport's ILS frequency at the radio panel (NAV)However, I can't find it at PMDG 747, only at the FMC NAVRAD, but I can't change the frequency. So what should I do if I want to have an ILS frequency different from the FMC

you need to put the complete rwy info in: (freq and OBS)e.g.:"112.80/078"

>you need to put the complete rwy info in: (freq and OBS)>>e.g.:>>"112.80/078">>Is that when I want to land at 19R vtbsI need to enter "109.5/195" under the line of "ILS-..."(forget) which should be 4L or 5L

correct. it should read something like "PARK/ILS". you enter the freq/obs right under it. i believe it is LSK L4:that should work. "109.5/195"