Honestly, that's something you're probably going to have to search for, for the exact details. It has literally been years since I've done it, and I don't remember all the details. If I recall, it's simply a matter of editing the model.dat inside the .zip files (in the Hytera CPS directory). I believe you find your model number in the model.dat files and simply edit the frequencies. So for example, if yours is 450 MHz to 480 MHz or such, there should be a 450 (or many of them) in plain text in that file. Simply change it to whatever you like, i.e. 420.
Hopefully someone else with more recent knowledge will be able to help with that. Also, I don't know if it works with the newer firmware. I'm still on 7 with all my Hytera gear.
Actually, looking through some of my files here, that's exactly what I did. So my model had the following bandsplit in the model.dat: Freq2=400,470,400,470,17 I modified it to show: Freq2=400,527,400,527,17 Like I said, it won't cover anywhere close to that, but I just needed a little bit.