The Course Admin can add an Extra Class/ Lecture to the course by tapping the + button on the course timeline.
In the following menu, add the date and time for the class. If you want to add multiple lectures that follow a weekly recurring pattern, click the button "This is a recurring class"
In the following menu, select all the dates on which the class recurs.
Please note that this is different from cancelling a class and hosting a make up lecture. You can learn more about that here.
If you need an extra lecture and you're not the Course Admin, please get in touch with the Course Admin to create a new class.