Undoing an Import

On a number of occasions, we have come across an issue where we need to “undo” an import and then “re-import”.  In the past, we’ve asked for your assistance but we’d like to learn how to do it ourselves (similar to how we tackled “scrapping in bulk”).  Is it possible for you to provide us instructions, with screenshots, on how to “undo an import”?  Please let us know.  Thanks.