Hi friend
Thank you for asking. Kindly refer to our official site to manual update the Android 8 firmware version. (WW-15.10.1810.275)
#Manual Update Guide
https://www.asus.com/support/FAQ/1009748/#ZC520TL Firmware Spot
https://www.asus.com/Phone/ZenFone-3-Max-ZC520TL/HelpDesk_BIOS/ *Please make sure to back up your data before updating.
Asus will continuously provide applicable updates to our products for 18 months from the device first become available on the market. For any devices launched over 18 months, there will no longer be any system updates and maintenance (including ZenUI Launcher).
Sorry for any inconvenience this may cause.Thank you for your understanding and support.