ZIP archive of 5.04 MB named only ld21b, with no brand, device type or content description given in the name. The code alone is not enough to identify the product reliably, so the archive should be opened and its files checked to find out whether it holds firmware, a dump or service documents. If it turns out to be a flash image, compare the part markings on the board, back up the original chip with a programmer before writing, and ensure the image size matches the memory capacity, otherwise it will not fit.
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 @gunvantrathore. Enginerys does not host this file.
How to open a .zip file
Compressed archive that every operating system opens without extra software.