WordPress Metaboxes and Yoast SEO plugin keyword analysis

I’ve developed a website that uses a custom post type for a large number of pages for the site. I did so so as to better organize the way content was added by not just myself, but other administrators. For said post type, I also created custom metaboxes to the same end. Sadly, I didn’t take into account that I should have left the WordPress default editor as the principal way to include the main content and as such, the Yoast SEO plugin now returns the following on all of these post types: Bad SEO score - The text contains 0 words. This is far below the recommended minimum of 300 words. Add more content that is relevant for the topic. even though clearly, the administrator (and likely, search engines) can see this content. I need to know if there’s a way I can enable the Yoast SEO plugin to read the field trmet_overview to gather the text/keywords so as to get a better rating.

My metaboxes were developed using online tools and not a plugin so existing plugin extensions for products such as Metabox.io or similar would not work for me.

I’ve considered either a PHP or jQuery solution, but have yet to find one.