The failed listing shows any individual lines of Gift Aid that have failed on a submission to HMRC. The reason is shown, and you can select an individual line by clicking on it, which turns it blue, and then clicking the edit icon.
To then clear an individual line from the list after editing to make it available for submission again, click the sweeping brush icon after selecting the line.
For ease with large lists, you can also reset the entire list. This is useful for things like changes to donor details, so if a postcode were wrong it would be best to edit this on the donor/constituent record itself, and then this will be picked up for all lines against that donor on the next submission.
See below the icons, from left to right they are; Clear individual selected line, edit individual selected line, delete individual selected line, reset and clear all lines, export list to Excel, export list to PDF, help (which brings you to this article).

If you select the option to reset your list you will see the following message appears:

This is explaining that when you reset the entire failed list everything will be removed from the list, including lines that you believe are there correctly. However, once you do a submission anything that should be on the failed list will go back there, and anything that shouldn’t will be submitted as expected. Please do not worry about clearing the whole list, nothing will be claimed that shouldn’t be when you complete your next submission.
PLEASE NOTE: If you clear errors where the postcode or other address information was wrong, but you updated it on the constituent ‘master’ record, then when the lines return to pending, they will likely show as blank. This is expected and not an issue, when a submission is made, for any lines of Gift Aid without complete address information, the system will copy the address information from the master record and the lines will be submitted without issue.