Call a plugin function from WordPress theme header file

wp-content / plugins / ultimate-member / includes / core / class-permalinks.php

namespace umcore;
class Permalinks { 
        function __construct() {
            add_action( 'init',  array( &$this, 'activate_account_via_email_link' ), 1 );
        }
}

I want to call this function & # 39; active_account_via_email_link & # 39; from wordpress / theme / header.php

My code so far:

$action = new umcorePermalinks;
$action->activate_account_via_email_link();

The error :
Fatal error: Error not detected: class & # 39; um core Permalinks & # 39; was not found. at /home/xyzz/public_html/xyz/wp-content/themes/university/header-frontpage.php:5 ​​Stack Trace: # 0