The only way I would know to approach this would be to provide another forms process that would allow a user to lookup a previous submission of a form and then create a process for resubmission, perhaps just saving as a new version over top the old form. The way to do the lookup could be by having workflow save the relevant form data out to a sql database which is then the source of the forms lookup OR if you want to get fancier there are examples on Answers here of how to create lookups directly into the metadata of the Laserfiche repository. That takes a bit more SQL understanding and the ability to figure out how LF metadata is stored in the LF database itself. For advanced development only, IMO. You'd likely want to create a SQL view that would find and display that metadata in a nice SQL view so it was easy to point a database lookup to. That's a couple ways I would approach this.