A 2.09 MB RAR file for board code 3CESL, with RH131 written without separators, which probably corresponds to the RH-13 line of revisions. The precise meaning of the trailing digit is not clear from the name, and the contents are not stated. Extract it and check what is inside before use. The 3CESL family has several revision packages, so confirm the exact revision silk-screened on the PCB before following any diagram, test points or firmware image found here.
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 @cyberlanelectonik. 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.
7-ZipWinRARThe Unarchiver (macOS)