the easiest way would be to download it from here:
Right under the video is a download link. You just have to upload the theme via the backend or copy the directory onto the ftp server.
If you want to create your own, go to wp-content > themes on your ftp and create a new directory.
You need a “style.css”, a “functions.php” and a (random) image to show it in the backend.
The first lines in the style.css have to be like the one on the downloaded child theme. It’s necessary to get it loaded.
The same with the first lines in the function.php. Copy them from the downloaded file or just use the one from us.
Important: You have to activate the child theme from your backend. Otherwise it wont work.