It would be good to improve the 'View imported files' page, so that there will be another page with review of 'Undo import'.
1. Go to Admin page.
2. Click on 'View imported files' page.
3. Click on 'Undo import' button.
Undo import process starts just after clicking on 'Undo import' button.
After clicking on 'Undo import' button, another page is displayed with short summary of file which will be reverted (number of transactions etc.) and 'Submit' button.