1. First, find your picture. Here's mine:
2. Click on the Retouch tool, it looks like this:
3. Go to your Tool Options window. Select 'Smudge' and make your settings close to mine:
4. Now play around with it. Make sure you smudge every inch of the picture or you'll have places where the lines are still fine.
5. I usually like to start out going vertically:
then horizontally:
then in random directions:
but you can do it however you like :)