How far in is the mistake? What type of mistake?
Take a look at the videos on this page under ‘Fixing Mistakes.’ You should find what you’re looking for there.
I am not brave enough to unravel. There have been times i needed to take out one row or so. Someone told me that you could unknit something.
You can. Just slip your left needle into the stitch that’s below the first one on the right needle–just put it in the loop. Then slide the stitch off the needle and pull the yarn out. You will have ‘unknit’ one stitch. Just keep doing that until you get to where you want to be.
For purl rows, slip the needle into the purl bump under the right needle and slide the stitch off.