Firmware for the A9000 receiver, version V8.29, dated 26 October 2021, delivered as an 11.2 MB zip. It is part of a release series covering several models with the same version, so the model match matters. Extract the package and review its contents before flashing through the update menu, a USB loader or directly to the chip. Compare the main board of the unit with the expected hardware and keep a backup of the original flash.
The button opens the matching file on RM Schematics, or a source page if it is not catalogued there yet. The original attachment is from @tvsoftwareworld. Enginerys does not host this file.
How to open a .zip file
Compressed archive that every operating system opens without extra software.
Built-in OS tools7-Zip