The firmware update has TWO PD updates. If you look at the firmware page, it has an ASCII art of two passes.
Have the HDMI in the rear and power in the front of the same side. (I started on the Left side)
After it reboots, during the color blink codes, put the HDMI in the other side’s rear socket. You should get video. Then you can watch the boot loop.
Then when it reboot, pull the power. Plug it into the front port on the other side with the HDMI. Power it up. You’ll then see it updating PD2 (or PD1 depending on the side you started with.)
I had the same challenge with mine going from 3.07 to 3.23. I’ve still to do 3.23 to 3.24 … that’s a tomorrow update. 
Once complete and back into Windows, you may find your Keyboard/Mouse or so non reponsive. Once into Windows, I ended up pulling the power. Putting my HDMI back to the rear left, power to front left, and key/mouse in rear right. After booting, it’s operational once more. One finally reboot … pressing F2 … and the BIOS shows me on 3.23. WOOT !!!
Again, I’ll take it to 3.24 tomorrow - starting with the left side connected. Then switching sides to the right side.
Hope this helps.
P.S. When checking the BIOS is 3.23, go into Advanced, then set Standalone Operation to Enabled. It speed up your reboots as it doesn’t bother to check things like the battery, case open, etc.