I got this from this link:
The standard way of using merge to undo the entire check-in works great, if that’s what you want to do. Sometimes, though, all you want to do is revert a single file. There’s no legitimate way to do that, but there is a hack:
- Find the version that you want using svn log.
- Use svn’s export subcommand:
svn export http://url-to-your-file@123 /tmp/filename
(Where 123 is the revision number for a good version of the file.) Then either move or copy that single file to overwrite the old one. Check in the modified file and you are done.