Upgrading to PHP 8 di themes issue

Trying to upgrade to PHP 8 from PHP 7.4 but when I do I get a warning at the top of the page:

Warning: The magic method OCDI\OneClickDemoImport::__wakeup() must have public visibility in […]/wp-content/plugins/di-themes-demo-site-importer/inc/ocdi/inc/OneClickDemoImport.php on line 128

How can I resolve this please?

The page I need help with: [log in to see the link]