Want to add custom post type for facebook feed

You need to add the post via function call wp_insert_post. where you need to pass the parameter of post type as name of your custom post type.

$wordpress_post = array(
'post_title' => 'Post title',
'post_content' => 'Post Content',
'post_status' => 'publish',
'post_author' => 1,
'post_type' => 'custom_post_type'
);
 
wp_insert_post( $wordpress_post );

Hope this helps