How do you remove a dermal anchor?

You need to go back to the piercer that performed it. If that isn't an option, go to a doctor. If it isn't that deeply grown in, removal is fairly simple. If it is (and that's what they're designed to do -- grow into your tissue), the piercer (or MD) will use a scalpel to remove it. The scarring should be minimal. That being said, if scarring is a worry for you, don't get it somewhere like your face.