Below is a copy of her post. You can find the original post at: http://www.alicekeeler.com/teachertech/2015/12/10/google-classroom-unsubmit-work/
When students “Turn In” work in Google Classroom the ownership of the document switches from the student to the teacher. The document becomes “View only.”
If a student accidentally submitted or they need editing access back at a later point thestudent can click on the “Unsubmit” button in Google Classroom. If the student has the document already open, they will need to refresh the document to be able to edit the document again.
Submission History
When a student submits work, unsubmits work or resubmits work this is documented for the teacher. In the assignment grading screen, choose “See submission history” beneath the students name in the right-hand panel.
Return Student Work
The teacher is able to return student work. Check the checkbox next to the student’s name and click the “Return” button at the top of the student list on the grading screen. It is my recommendation to not do this for students who accidentally submitted. When students request access to their own documents, I indicate that they can click on “Unsubmit” to regain access to the document.
Keeler, Alice. "Google Classroom: Unsubmit Work." Teacher Tech. N.p., 10 Dec. 2015. Web. 10 Dec. 2015.