If you want to install the firmware directly through the phone's system updater:
Official links from Huawei have largely been decommissioned for this model, but you can still find community-hosted archives: 4PDA (Huawei Mate 8 Section) huawei nxtal10 firmware link
is often used to "rebrand" international Mate 8 models (like the NXT-L29) to access EMUI 8 (Android 8.0), as Huawei only released that update for Chinese versions. If you want to install the firmware directly
Power off the device, then hold buttons simultaneously to trigger the automatic update process. huawei nxtal10 firmware link
Huawei Mate 8 Dual SIM TD-LTE 128GB NXT-AL10 (Huawei Next) | Device Specs | PhoneDB. PhoneDB.net HUAWEI S-TAG:Version update | HUAWEI Support Global