I apologize if I misunderstood your question.
From the student dashboard, your students should be able to see the CSP course tile.
From the teacher side, you can control how much (or little) of the course they can see. Depending on what you have made visible, students can select units and then lessons. This is the menu from Unit 1.
Once in a lesson, students can also use the menu at the top of the screen to jump from lesson to lesson using the 'more' orange triangle drop-down menu.
They should also be able to start in Lesson 1 and use the orange continue button on each level to move from activity to activity.
The top tile on their dashboard has a continue button that takes them to the last lesson they were working on.
If none of these options are working, there may be a bug that needs to be report to email@example.com.
You can also provide your students with a direct link to U1L3: https://studio.code.org/s/csp1/stage/3/puzzle/1
Hope that helps!