By default, Blackboard assignment allows single attempt. Yet your instructor may allow you to submit an assignment more than once for a variety of reasons. You should go through 'Assignment Information' before submitting the assignment. Your teachers might indicate the number of attempts allowed there.
This article suggests what you can do if you would like to submit an additional attempt to an assignment.
Submit a new attempt
If an assignment allows multiple attempts and you have not used up the number of attempts, you will see a 'Start New' button on the 'Review Submission History' page. You can start and submit a new attempt then.
To access 'Review Submission History' page, click on the assignment link. Please refer to Blackboard Help: Resubmit an assignment for more information.
Remember to check if your assignment was submitted successfully (Blackboard Help: How do I check that my assignment was submitted?) after the submission.
Please note that students cannot delete or overwrite previous submissions.
Request an additional attempt
In case the assignment allows single attempt or you have used up the number of attempts, you are advised to contact the Instructor and TA and see if they would like to allow additional attempts or ignore/clear the wrong attempt for you. If they have questions about those features, they are welcome to contact us at ITSC Service Desk (https://servicedesk.itsc.cuhk.edu.hk) or firstname.lastname@example.org and we will follow up with them.
If your Instructor or TA allow you to submit a new attempt, after submitting it, remember to check if your assignment was submitted successfully (Blackboard Help: How do I check that my assignment was submitted?).