Is there a tool that can batch edit the image's EXIF data and copy the keywords and put it into description field?
Sure. You could easily do this with ExifTool. Something like
exiftool -'imagedescription<keywords' *.jpg
imagedescription is the tag you want to copy into and
keywords the tag you want to copy from. The
< is the copy tag value operator.
Note, though, that there are a number of different standards for this kind of metadata, and you might find that your keywords are actually XMP Subject tags or something else depending on what software put them there. (Exiftool can handle this too -- you'll just have to figure out exactly what the tag names you want are.)