Is it to change the negative you left for a positive? Has the matter been fully resolved? Do not change it on any promise from the seller, just open a case for item not as described if the item is not working, to receive a full refund.
If the matter, and only if, it has been fully resolved, then message the seller for a feedback revision for you to complete.
Positive feedback cannot be changed, but here, do not wory if you need to open a case for that item, as feedback is not taken into consideration, as it can be left in error.
Just to say , you mention refund in your neg feedback, this actually breaks feedback rules, and the seller if they knew these rules, could ask for your feedback to be removed.
