I would start by trying to find the uncompressed version of the file (probably called richtext.js). If you find it, I would look at correcting it within that file, then regenerating your richtext_compressed.js file (using something like YUI Compressor [developer.yahoo.com]).
If you can't find it, then there are still formatting tools you can use to format richtext_compressed.js to be more developer friendly. For example, [jsbeautifier.org...] Note, if the compressed version replaced variables to be shorter, then it might still be difficult to understand exactly what is going on (trying to understand what a variable named "A" is supposed to represent may not be entirely obvious). But I'd search for "style" or "body" to try and find that bit of code within the script, and focus on only the section(s) that matched. When you're done, don't forget to compress it again with YUI Compressor.