Once you have verified you have the correct .bin or .img file for your specific hardware version:

The FiberHome HG6243C is a popular router model used for fiber-optic internet connections. Updating the firmware of your router can improve its performance, security, and stability. In this guide, we will walk you through the process of downloading the firmware for your FiberHome HG6243C router.

HG6243C Modem Specifications and Features | PDF | I Pv6 - Scribd

serving as a widely used GPON ONT (Optical Network Terminal) for triple-play services. Official Firmware Sources

Instead, here is a regarding firmware for the FiberHome HG6243C.