How to disable wordpress yoast seo plugin on external pages?

I'm running my wordpress website with a child theme. I use my own external pages and include wordpress with "require('../wp-blog-header.php');" on these pages. The installed yoast seo plugin is loaded, when I include this header. Now I want to disable this plugin on my external pages. How can I achieve this in the functions.php file of my child theme?

via Chebli Mohamed