Hello @karen_s_thorpe 
Welcome to the Canvas Community. This past April, I helped answer a very similar question. So, I would like to point you to: DELETING STUDENT SUBMISSIONS. Your student(s) should be able to re-submit an assignment to you without issue. (See the section called "View Submission" in How do I submit an online assignment?.) From their perspective, they always see the latest submission. But, you as an instructor have access to all submissions of the particular assignment...which are all time/date stamped. (See the section called "Evaluate Multiple Submissions" in How do I view the details of a submission for a student in SpeedGrader?.)
I hope this information will be of help to you, Karen. Please let Community members know if you have any questions about this. Thanks!
