Yoast noindex on some search results

I’ve chucked my site through a website checker and it’s told me that some pages have become non-indexable. This is only since I’ve installed Yoast. They are searches, like the above /?s=Swan . The Yoast settings are already set to ‘Show Posts in Search Results’ so that’s the most important one enabled that I can see.
Another Google Search has shown the following solution:

Admin > [content-type] > Edit > Yoast SEO metabox > Advanced (gear icon) > Allow search engines to show this [content-type]

But I can’t see where that is in my admin! Any help with finding the above? Or any other suggestions? It’s important that these search results appear to Google!
Thanks