Unfortunately, Yoast incorrectly implements this and there isn’t a “domain” field in the settings in WordPress admin. However, you can change the content of twitter:domain by adding this to your theme’s functions.php file:
add_filter('wpseo_twitter_domain', 'override_twitter_domain');
function override_twitter_domain($domain) {
return "blog.millerostock.com";
}
Clear your site’s cache, refresh the page, and you’ll see it in the source.