eBay will not remove that feedback as it doesn't break any feedback rules.
All you can do is to try and appease the buyer. Send them a polite message saying you are very sorry the item was not as expected, and could they explain what was mis described, or what they found not to be accurate, and you can perhaps ( this only if you agree to add ), discuss a partial refund or a full refund on return of the item.
If you can come to some agreement, perhaps then, they would agree to complete a feedback revision you can send to them.
None of the above is guaranteed to make that change but it's the only way to try and have that feedback removed, and that's in the buyer's hands.
@joannas521
