Hi,
You should create an override as explained here: https://docs.acymailing.com/developers/create-a-page-override
The filename for the unsubscribe page is unsubscribepage.php.
For Joomla it's located in /public_html/components/com_acym/views/frontusers/tmpl
I don't use Wordpress so I can't tell you exactly where that file would be located. It should be somewhere in the folder path wp-content/plugins/acymailing/front, If you can't find it you can use a ftp client like Filezilla to search for the file on your server.
