On the page https://www.schemaapp.com/wordpress-plugin/faq/, under the Yoast SEO FAQ, it states “Leave the SearchAction in place.” Where is this SearchAction?

For Yoast SearchAction, they don’t provide a way to disable it from their settings. This is why you are unable to find it. However, there is a way to use a WordPress Hook / Filter within PHP, but it is not worth the effort as it’s a fine implementation of the schema markup.