It actually not that hard to update it manually once you know how
The way i use is checking first asus website for updates at ROG Phone II BIOS & FIRMWARE | Phone | ASUS Global
And then check on
Steps of Update:
1. Check software version of your device**
2. Download device software and Update SOP (From “Manual” Item)
3. Only apply to same SKU update, Example: WW->WW, CN->CN, TW->TW.
4. Software update cannot transfer the software SKU and downgrade the software version.
5. Wrong SKU may cause update failure, please update the same SKU version only.
**How to know the device model?
Path: Settings->About-> Model number
Example: ASUS PadFone2
**How to know the device software version?
Path: Settings->About-> software information->Build number
**System upgrade may cause part of data missing, please buckup your important data before system upgrading.
Once you find out which sku your phone has, download it latest update if there is one and put it on the internal storage then restart your phone if needed after disconnecting the usb a notification should popup about new update