If you are looking for a , these are often found in the "README" file within the same directory, on the download page's comments section, or by searching the filename on the site where you originally found it.
Be cautious if this file was downloaded from an untrusted source. RAR files with cryptic hexadecimal names are sometimes used to distribute malware or unwanted software. dc87a445955547ac9d2ac1829784ea86.rar
To help you find the "piece" (likely a missing part of a multi-volume archive or a specific password/key), could you clarify a few details? If you are looking for a , these