Android application package, version 5.7.4, whose Chinese name refers to a video and movie streaming app. It is not repair documentation, firmware or a schematic, and it has no relation to any motherboard. The 2.29 MB .apk is installed on an Android phone or TV box, either by sideloading or through adb. Files from unofficial sources can carry malware or unwanted permissions, so scan the package before installing it. It should not be used on devices handling sensitive data, and it is of no use for board diagnostics or flashing work.
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 @tv_software. Enginerys does not host this file.