Run this short SQL query through PHPMyAdmin.
UPDATE wp_posts SET post_type = ‘page’ WHERE post_type = ‘post’
MyPhpAdmin > posts > SQL > paste code
Change to your post format – my_posts and GO
Change back:
UPDATE wp_posts SET post_type = ‘post’ WHERE post_type = ‘page’
But – all pages would be converted into posts. Never tried it for one post or page.