To add a non recurring class to your Class Schedule:

In the left side menu in your admin site, select Schedule/Classes > Add Non Recurring Class > fill out the form.

The difference between adding a class and adding a non recurring class is simply that Triib asks for the date on which the non-recurring class starts, but does not ask for recurring days of the week, as the class ends after the scheduled date.

NOTE:

This is the best set up for bi-weekly classes as the recurring class option is only for weekly.