"Put the yarn in back (that's the yo)
then put the needle in the same three stitches and purl them again and slide them off the needle. The yarn will come up over the back and make a yarn over extra stitch."
Sorry, I'm trying to see it. What do you mean by put the yarn back in and put the needle in the same three stitches? Is the needle already in the same three stitches because you did not slide them off?