 To give an extension to students, you can change the due date of your assigned assessment. Under the administration tab, click on assessment settings. Here I can change the due date to a later date, change the time, and even change the lateness penalty. Once I click save, I can see that it will be updated here. And if I click on the students tab, I can see what the student would see when they go to submit by clicking on the submission link beside a student's name. Here's the revised due date and time, and if I click on this, I can see the lateness penalty that will be applied.