If you need to un-submit your SSEC form, use the "Make Changes" button at the top of the form.
Then, choose the question you wish to edit by clicking on the "Application Pages" button.
Make the necessary corrections and then click "Save". Continue pressing the "Save" button on every question all the way through the last question (Person Completing Form).
You will again see the "Saved" screen, and then you will need to click the Attestation and the "Submit" button at the bottom of the page to re-submit your form.