Is is possible to edit existing submissions?

Is there any way to have a form recall an earlier submission and change a value, then resubmit?

Yes, that is possible, please follow this guide: https://www.jotform.com/help/325-How-to-Edit-Submissions-Made-on-Your-Forms

You can allow your submitters to edit the submissions as well: https://www.jotform.com/help/40-How-to-Let-Users-Update-Their-Form-Submissions-at-a-Later-Date

Hope it helps.

Let us know if you have any further questions.

Thank you!