I couldn’t download blender 2.80… Only blender 2.83 is available
Welcome to the website. 
I see that you’re asking about Blender but have marked this in the “Unity courses” category. Remember to check the category when posting so that you’re sharing your work with the right audience.
You can download previous versions of Blender by following the “Previous Versions” link on the blender.org “Downloads” page, or by Googling the particular version. Version 2.80 is available here: https://www.blender.org/download/releases/2-80/
You should be fine to use Blender 2.83 for the Blender courses here though.
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