How to Edit a Form on submitted by a user?
An Editor who has access to the form can edit the submission made by a user
Goto Left Menu >> Editor >> Forms >> View All Forms.
Select the form you want to edit and go to the analytics page for the form by clicking on the Analytics icon.
Then select the user whose form you want to edit and click on the view icon on its right side.
Click on the EDIT icon at the top right corner to edit the form.
Make the changes you want to make here on this page.
Click on Submit icon when the editing is done.
This is how you should edit the form on behalf of the user.
Note: If the form has - Need Approval Enabled, then the form can be edited by the editor only before its approved/rejected by the approver.
When you click on the View icon, here on this page you can also Approve/Reject the form as well.