You can post one follow-up to feedback you left at https://feedback.ebay.com/ws/eBayISAPI.dll?ReviewFeedbackLeft. You can also go to your own Feedback Profile (click your own feedback score--the "(7)" behind, or on this page 2 lines under, your username), switch to the "Left for others" tab and for each one that you haven't already left a follow-up there is a link to do so.
If you mean you want to revise the rating and comment a less-than-positive that you left for a seller, the seller has to invite you to do so (and s/he has a very limited number of times per year that s/he can do so).
Don't leave feedback to communicate with* or in any way try to get the seller to react to it. Feedback is for future potential trading partners of the user you leave it for, and you should wait until all issues with the transaction are settled finally one way or the other or in between. When an item arrives damaged you ask for a return at the seller's expense (or partial refund to keep it) from the seller and if s/he doesn't agree from eBay and follow through ("Ask eBay to step in" when the seller doesn't satisfactorily respond within 3 days of asking for a "return" in your Purchase History) until you get a return label paid by the seller or a satisfactory refund. THEN you can leave feedback on your opinion of whether the transaction as a whole is positive, neutral or negative (come back here for advice on wording the comment if you had to open a return through eBay as there are tricky rules about mentioning such an "investigation").
*other than a positive that you got the item and are happy with it
