To set default author in WordPress add the following code to any code snippet plugin such as WP Code or Code Snippets
function set_default_author( $data, $postarr ) {
// Check if the post is being created
if ( 'auto-draft' === $postarr['post_status'] ) {
// Set the default author ID
$default_author_id = 2; // Replace with the user ID of the desired default author
// Set the post author to the default author
$data['post_author'] = $default_author_id;
}
return $data;
}
add_filter( 'wp_insert_post_data', 'set_default_author', 10, 2 );
To change author you can change author id. read this blog to know author id