Yes, users can edit their submissions even after they have sent them. To enable this feature, open the Advanced section of your form.
Tick the option Allow respondents to edit delivered submissions at a later time.
After clicking the Submit button, on the Thank You page, form users will receive a link and instructions for using it.
When that link is accessed, the form opens up in a lightbox. Form fields contain the input users have provided and all content is editable. After making edits, users simply need to click on the Update Submission button to have the new content saved.