You can browse the ZTE Support Document Map for historical manuals and known solutions, though direct firmware files for EOS products are rarely listed for public download.
If you have successfully obtained a .bin or .img firmware file, follow these steps to install it: Notice:EOS Announcement for ZXHN H267A V1.0 - ZTE Support
Because firmware is often customized for specific ISPs, using a generic version can sometimes disable your internet connection or VoIP services.