If your end user has released a landed costs invoice which was entered incorrectly and now requires to be corrected do use the Reverse option under the actions button of the original landed costs invoice.
If you use this option then the stock item cost will not be corrected.
To ensure the stock item is corrected you need to create a new AP debit adjustment and on the landed costs tab link to the original PO. Once this debit adjustment has been entered and released you can re-enter the landed cost invoice and your stock item costs will be correct.