1. Add this code to your php snippets

add_action( ‘wp_head’, function () {

$schemamarkup = get_post_meta(get_the_ID(), ‘schemamarkup’, true);
if(!empty($schemamarkup)) {
echo $schemamarkup;
} );

2. Turn on CUSTOM FIELDS from page/post settings.

3. Use Google’s Structured Data Helper to create your code for you.

4. Create a Custom field called schemamarkup on your page and paste in the script you created in google