Downgrading an ASUS ZenFone 5 typically involves manually flashing an older firmware version. This process is most common for rolling back from Android 10 to Android 9 or moving from Lollipop to KitKat on older models.
Install ASUS Android Drivers and ADB tools on your PC. Zenfone 5 Firmware Downgrade
You must use firmware that matches your device's SKU (e.g., WW for Worldwide, CN for China). Mixing SKUs will cause failure. Method 1: Using MicroSD Card (Recommended for ZE620KL) Downgrading an ASUS ZenFone 5 typically involves manually
Once complete, select "Wipe data/factory reset" , then "Wipe cache partition" , and finally "Reboot system now" . Method 2: ADB Sideload (For Older Zenfone 5 Models) WW for Worldwide