It depends on the bootloader. Some versions block downgrades. If allowed, same process.
The file will typically be named something like: ZTE_F671Y_V2.0.0B10_General_2024.zip . Do not unzip it unless instructions specify. zte f671y firmware update portable
ZTE F671Y Firmware Update: A Portable Guide to Enhancing Performance and Security It depends on the bootloader
The router will upload the file and begin the flashing process. zte f671y firmware update portable