You can easily revert any task to it's pre-edit state, as long as it's still backed up - 30 days or more depending on the plan. The maximum is 360 days for the Enterprise plan. For more information, please visit the Plans and Pricing page inside the app.
Reverting a task simply re-uploads the before images of that task. If you edit an image with multiple tasks and want to undo them all, simply revert the first task.
To revert, simply open One-Time Tasks and click on the revert button associated with that task. Please note that it is not possible to revert specific images - revert will re-upload all images in that task to the pre-edit state.