The negative is too old to do anything about, but I agree with @red_magpie the neutral may well have been left by mistake, easy to do.
Send the buyer a message asking if they would kindly complete a feedback revision to complete.
If they ignore the message, then the neutral will not affect your seller performance or feedback score, and anyone caring to read it, can see nothing detrimental was written, in fact the opposite, indicating it was left in error.
@uniquestuffstore