How to unapprove an approved journal entry.

We have had situations where a journal was approved and then the approver realized there was an issue with it, that it should not have been approved. We have gone to the approval tab and tried to change the approval action to none and deny, but it doesn't un-approve the transaction. We have had someone make changes to the journal, edit journal, change the journal back, edit journal and the journal still shows it is approved and isn't being routed again. If the user submits again, it shows it is already approved.

What method do you use to un-approve a journal that was already approved?