1-Download the 9.0.0 (PQ1A.181205.006, Dec 2018) file from
https://developers.google.com/android/images
2-Unzip the contents of the zip into your ADB/Fasboot folder (I just leave my ADB folder on the desktop, windows 7). This is assuming you downloaded ADB/Fastboot program for Windows.
3-Right click and open the flash-all.bat file with a free program called Notepad++ and remove the last part of the text that says "-w" and SAVE FILE.
4-Remove the Edge sense module from Magisk on your phone if installed.
5-Make sure the phone has USB debugging enabled and USB cable plugged in with FILE TRANSFER mode turned on.
6-Run command in ADB/Fastboot:
adb reboot bootloader
click on adb flash-all.bat [now that its modified with -w removed. If -w was not removed, the phone will be WIPED CLEAN!]
(phone will restart) Go back into ADB/Fasboot:
adb reboot bootloader
adb fastboot boot <insert_name_of_TWRP_image_here>.img
7-Once in TWRP, FLASH your TWRP.ZIP and restart into Recovery.
8-Flash Magisk, other stuff etc at this point.
There is no need to remove Magisk or Unzip the secondary file inside the OTA. I've done it without those steps and nothing was changed.
I did re-install the latest version of Edge sense in Magisk as he put out a new version that works with the latest DEC update.