read about changing feedback in the ebay help:
http://ocsnext.ebay.com.au/ocs/sc
If you left negative or neutral Feedback that was intended for someone else, we may be able to remove it.
Here's what you need to do:
- Leave the same Feedback for the correct member.
- Contact us to let us know about the mistake.
In fact, you had better read the whole policy and tutorial on feedback - you are not allowed to leave a false positive for a buyer for instance.