From my Instagram post on how to bypass the read passwords on a Hytera you purchased second hand, see the guide here on how to place your radio into download mode to update the firmware. https://www.hamdigitaal.nl/download/algemene-informatie/DMR&PDT%20Subscriber%20Firmware%20Hytera%20Upgrade%20Guide%20R7.0.pdf
This specifically covers models up to the PD782 and says its for firmware v7.0, but the instructions to get into download mode are the same for newer firmware versions. If/when I find a guide detailing this process for newer models, I'll post it here.