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If I understood you correctly you wish your users to be able to update the submission without having to fill in the form again.
If this is correct then you can include an edit link on an auto-responder. When they fill in the form they will receive an email confirming the submission and with the edit link they will be able to update it at anytime:
You can see here more details on how to create an auto-responder:
Let us know if we can assist you further.