Extend Schema.org Types options of the WordPress Schema plugin https://schema.press/docs/adding-support-new-schema-org-types/

schema-wp-add-new-type.php

<?php //* do not include php tag

add_filter( 'schema_wp_types', 'schema_wp_new_add_schema_type_7623456' );
/**
 * Add New type to Schema Types options
 *
 * @since 1.0
 */
function schema_wp_new_add_schema_type_7623456( $options ) {
	
	// Change 'NewType' to the actual schema.org type you want to add
	// Example: Event, Product, JobPosting, ...etc.
	$options['NewType'] =  array ( 
						'label' => __('NewType'),
						'value'	=> 'NewType'
						);	
	return $options;
}