You can download the start assets from the GitHub release as shown in the video here: https://github.com/GDquest/Your-First-Game-Godot-2d-Platformer/releases/tag/1.0.0
Note that the start-assets/ folder is also included in the create-your-first-game-platformer-2d-godot-projects.zip archive you may have downloaded in the previous page, Download all the Godot projects
