Yes, you can undo the accidental "sold" status on an item. There are two ways to do this.
Option 1 - Void the invoice
The best way to return the item to "For Sale" is to void the invoice. This approach will:
Ensure your Sales records are accurate.
Return the artwork to "for sale" and increase the inventory quantity by 1.
1. To void an invoice, go to Sales > Invoices, and click the more options icon (...) next to the invoice you want to void.
2. Select View Invoice.
4. Scroll to the bottom and click Cancel Invoice:
4 . A pop-up window will appear to ask "Are you sure?"; click Yes.
The invoice will now be marked as voided:
Option 2 - Manually adjust the artwork status
The other option (if you've deleted the invoice, or don't want to void it for some reason), is to manually adjust the status of the artwork from Sold to For Sale, and then change the quantity from 0 to 1.