Google Spreadsheets : Edit form responses after you submit them in Google Spreadsheets
If the creator of a form has enabled it, you can now edit your response to a form after you’ve submitted it.
– The creator of the form needs to enable the new checkbox ‘Allow users to edit responses’ to allow respondents to edit their responses after they’ve submitted the form.
– If your username is being collected by the form and you check the ‘Send me a copy of my responses’ option, then there will be a link to change your responses in the confirmation email that you receive.
– You can also edit your responses on the form submission confirmation page. On the confirmation page, click the ‘Edit your response’ link.
For more information: