When forms need re-exporting, this can be done by going into the case and selecting the Export Logs tab.

Forms can be re-exported for all current cases and archived cases up to 12 months old.

In this example, one of the exports has reported an error:

To the right of screen is the Actions button:

Select the files you wish to re-export, and Confirm:

The Export will be Queued:

And shortly a confirmation message will be displayed: