Reach out and offer the refund first. Then once refund is complete then try to see if you can have them alter or remove.
Be careful when dealing with negative reviews. Recently, a member got a 1 star turned into a 4 star when he responded to the customer and displayed over the top customer service to the customer in question.
We would recommend you reach out with a similar toned message to what he recommended here, it could go something like this:
Dear (CUSTOMER NAME),
My name is (YOUR NAME) & I'm the CEO of (SELLER ACCOUNT NAME). I'm taking the time to personally contact you today as I see you've had a negative experience with our (ITEM NAME).
First off, I'd like to let you know that we care deeply about your experience with our items and sincerely apologize for this.
I completely understand why you posted your review. Negative reviews significantly affect the performance of our products on Amazon, this is why we take such care to make sure that we source the very best quality products and provide them at the very best prices possible.
If there's anything I can do to help remedy this poor experience, please let me know how I can be of service.
Finally, I'd like to thank you for taking the time to flag this with us and also for reading this message.
Kind Regards, (YOUR NAME)