CRDOWNLOAD format is used to store partially downloaded file initiated through Google Chrome. These files should actually be deleted/renamed, but sometimes their remain in the default download location. Unfortunately, there is no way how you could anyhow recover data from .crdownload file and get at least partial .mkv file from it. You have to download the whole file again.
Videos that are almost download could be played with simple extension renaming, but they will be corrupted in most cases with only some parts might be playable.Open CRDOWNLOAD file Open MKV file