Since official ASUS support pages may no longer host the direct .raw file, users typically rely on the following community sources:
Connect the phone to a PC, load the .raw file into the flash tool, and select the appropriate model (Z008 for ZE550ML) to begin the flash. Download ZE550ML 311 20170609 raw
Put the phone into Fastboot mode by holding Volume Up + Power . Since official ASUS support pages may no longer
Provides firmware databases and guides for downloading official stock ROMs used for system restoration. Download ZE550ML 311 20170609 raw
Community-maintained lists like the All Firmware ASUS Zenfone update thread often contain historical links to specific versions.
Flashing a .raw file is typically done when the device is "bricked" or cannot enter standard recovery: