How can the user update/modify a previous submission

If you would like to allow users to return to their submission at a later time to make updates, send an edit submission link in an email autoresponder:

https://www.jotform.com/help/40-How-to-Let-Users-Update-Their-Form-Submissions-at-a-Later-Date

If you want to send an edit submission link for a previously entered submission, it is possible to extract the Edit Link as long as you know the Submission ID. Here's an example of an edit submission link:

https://www.jotform.com/edit/353303246922134929

You just need the URL (https://www.jotform.com/edit/) and the (submission ID). The submission ID can be found on the Submissions page. Here's how: