By following this guide your warranty is void obviously and you will lose all data0. Go to settings, accounts, remove your google account
1.Go to https://www.asus.com/tw/Phone/ROG-Phone-II/HelpDesk_Download/
Download vbmeta.img
https://drive.google.com/open?id=10DzVAr_HDc95jPYXkb0O6ZWf7f8FoIg1
Download the most recent GSI
https://github.com/phhusson/treble_experimentations/releases
(ensure it is system-quack-arm64-ab-gapps.img.xz if you want google apps or system-quack-arm64-ab-vanilla.img.xz if you don't)
Extract the .xz file
2. Load up the apk from Asus
3. Agree to terms
4. Press unlock (you must be on wifi)
5. Wait until the device is back at the initial setup
6. Power off
7. Hold down vol up + power until you are at a screen which says power off/reboot/enter recovery/restart boot loader
8. Ensure you have adb and Fastboot setup
8a e.g. on a Mac
Open a terminal run
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
then after
brew cask install android-platform-tools
9. Connect a USB to the phone via the side port/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
then after
brew cask install android-platform-tools
10. Check Fastboot is working
fastboot devices
11. If you can see your devicetype the following
fastboot --disable-verity --disable-verification flash vbmeta
Leave a space after vbmeta, then drag and drop the vbmeta.img file into the terminal window
12. If successful
type
fastboot erase system
13. Type the following
fastboot flash system
Leave a space after system, then drag and drop the extracted img file NOT the xz into the terminal window
14. Wait
15. Once done
16. type
fastboot reboot
17. Wait
18. BOOT WILL FAIL
19. Use the arrow keys and power to select factory reset
19. Use the arrow keys and power to select Yes
Your device will now boot into current android.
Thanks to @suzook and @reg66 for pointing me in the right direction.
