Is it possible to create a form that can be updated by the person completing the form?

Hello FNSW_Referee,

I am not sure if I have understood your question correctly. Do you mean to say that you want to allow users to update their own submission data? 

Yes it is possible to achieve your requirement by taking advantage of "Edit Link" feature and adding it in your form's auto-responder email alert. This will add a clickable link in in the auto responder email user receives which will allow users to edit their own submission data. You may like to take a look at the following guide which should help you:  https://www.jotform.com/help/40-How-to-Let-Users-Update-Their-Form-Submissions-at-a-Later-Date

Hope this helps.

Do get back to us if you have any questions.

Thank you!