How do I change the author of a custom post type?

in Custom Post Type register arguments array use this

'supports' => array('title', 'editor', 'thumbnail', 'comments', 'author'),

This will activate author box on the edit screen. After registering author to cpt you need to activate author from edit screen option ( top of the edit screen where you can enable/disable all metabox ) to display authorbox on the edit screen.