Usually the start of the tutorial has a “Training materials” link and there is a zip. The planets zip has some cinemachine stuff you need but no prefabs as the tutorial then asks you to insert.
Working with Cinemachine link
Setting up Virtual Cameras: Stage 1
Unity Course Devs state:
Import the planet package.
Create Skybox in Lighting Settings
Add the planets prefab to the scene.
With the Mark as complete button below it.
Of course if you cant have the zip file you cant do the Tutorial. There are other posters pointing this but Unity Devs havent seemed to reply yet.
This one has been driving me nuts too. I’m running 2019.3.8f1. After importing the planets zip, In project window, navigate to Assets\Scenes\Final. Double-click on ‘Complete Scene’ in Project window to open. Then Create an 'Assets/Prefabs Directory, and drag the Earth,Jupiter, Neptune and Sun objects from the ‘Complete Scene’ Heirarchy window into the Prefabs directory, saying you wish to create a new prefab, if prompted. Then you have created planet prefabs, which you can use by dragging them into your new, empty scene, from the Assets/Prefabs Directory. Bit late replying but I hope this helps JohnG
JohnG