Trying to go off memory for what I did to reset the TPMS threshholds.
Hold the Back button on the left side of the steering wheel while pressing the Cancel button on the right. When you get to the TPMS setting, press the Cruise On/Off button while holding the Back button. That will get you into the TPMS settings. Once in the settings, adjust the TPMS numbers to what you want. Front and Back pressures are two different settings. When the number is where you want it, press the On/Off button to lock it in. After you move through the settings, they recommend that you reboot the system.
It took me a couple of tries to get it to stick when I adjusted the pressures on my 21, but it does work. And no, I didn't need the PIN from the dealer.