To edit invoices, click on the bidders name and clicking the edit icon next to that invoice.
1) Click "Auctions" on the far left > Click on "Manage Auctions"
2) Click on the "Name" of your auction.
3) Click "Invoices".
4) Click on the Bidder's name of the invoice you want to edit.
5) Click on the "Pencil" icon to edit that selected invoice.
6) From here you can Discount an invoice if needed