You may find that a student has submitted an assignment, but then want to change the file that they originally uploaded.
To best facilitate this, you should make sure that an assignment allows students to re-submit by setting the “Number of Attempts” to multiple attempts. You should also make sure that the assignment settings under “Submission Details” is set to “individual”.
You can learn more about changing assignment settings in Blackboard here.
If the problem persists, please submit a ticket detailing your problem at: https://servicedesk.cit.ie