It is possible to add a yogi to a class without a valid membership or class pass. The yogi is registered now for this class as 'unpaid'. If you want to change this from 'unpaid' to 'paid', for example, if the yogi has purchased a new class pass, you can do so by following these steps:
Go to the class you want to change the attendance of the yogi.
Delete the yogi from this class (you can do this for future and past classes as well). Make sure the yogi has a valid membership or class pass for this class and re-add the yogi to the class. You will note the text has changed to 'paid: yes'.