In the app there is a box called "completed". The students need to fill it out themselves if they want to be able to use the "Resume the course" button.

I wish the lesson would be marked as done automatically, when the student has done the quiz or survey in the class. If the lesson is only a text or a video, it should be marked as done immediately, I guess, as there is no way to know if the student has read the text or seen the video. Please <3