If you using phone app... Hit update and add more photos then hit update at bottom.
If you are using website, click EDIT on your listing.
I think at some point close to the end of the auction you can't edit or update. So it may be too late.
FYI in your future auctions you will get a lot more bids with lots of good photos... Especially if you are new, photos and NOT stock photos will help you sell.