ASUS archive labelled P5405CSA with revision R2-1, a 7.76 MB RAR whose name gives no file type, so it may hold a BIOS dump, schematic or boardview for that board. Extract and check the contents before relying on them. Match the model and the 2-1 revision against the markings on the motherboard, since ASUS revisions can differ in components and rails. For any firmware inside, read and keep the original SPI contents with a programmer before writing, and confirm the image size equals the chip capacity.
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 @boardsscanrepo. Enginerys does not host this file.
How to open a .rar file
Compressed archive — the usual wrapper for a schematic + boardview pair or a BIOS + EC set.