Looks like there's now a way to manually update for those of you who don't have unlocked bootloaders.
Have a read of the last few pages in this thread https://forum.xda-developers.com/mate-20-pro/how-to/guide-manual-updating-firmware-t3893171
Basically download the firmware in the OP of the thread and use this tool https://www20.zippyshare.com/v/ysCf7h16/file.html
Have a read of the last few pages in this thread https://forum.xda-developers.com/mate-20-pro/how-to/guide-manual-updating-firmware-t3893171
Basically download the firmware in the OP of the thread and use this tool https://www20.zippyshare.com/v/ysCf7h16/file.html