In your wordpress project's composer.json file, add this under repositories and make sure you already added and install the parent theme:
{
"type": "vcs",
"url": "git@github.com:jantinnerezo/blangko.git" // Parent Theme
}
{
"type": "vcs",
"url": "git@github.com:jantinnerezo/blangko-child.git" // Child Theme
}
After that you should require it to your wordpress project's composer.json file:
composer require jantinnerezo/blangko-child
Go to: Appearance / Themes and then activate the blangko-child theme and you're all good!