Hi Kevin,
May I know do you want to change the text or entirely page?
If you want to change the error text (which is not advisable-it is make some difficulties when come to troubleshoot issues) you can do language override in for the language constant below:
COM_EASYBLOG_PRIVACY_NOT_AUTHORIZED_ERROR
If you want to customize the page itself you can follow Joomla documentation here:
https://docs.joomla.org/Custom_error_pages