<?php //* do not include php tag
add_filter( 'schema_output', 'schema_wp_override_description_yoast_seo_12345' );
/*
* Override Schema description value with Yoast SEO description
*/
function schema_wp_override_description_yoast_seo_12345( $schema_output ) {
// get description value from Yoast SEO post meta
$desc = get_post_meta( get_the_ID(), '_yoast_wpseo_metadesc', true);
// override the value in schema output
$schema_output["description"] = $desc;
// return our schema array
return $schema_output;
}