Whilst there are some circumstances in which you can 'back out' an import, we recommend avoiding having to do this by checking your import thoroughly before accepting it.

An import can only be undone within 30 days of it having been approved.  To undo it, open the relevant import record on the Import Landing Page and click Undo. 

There are some circumstances which will prevent you from undoing an import.  For example, if you've imported Products which have been used within other records, such as within an Opportunity or a Sales Order, you will not be able to undo your import.

To save using unnecessary space on your database you should consider deleting your import records once you're happy that you do not need to undo the import. It's good practice to delete any records with a status of Not Run. If you have any import records with a status of Awaiting Review but you know you will not be approving the import, these too should be deleted.