BuddyPress.org

Just create a child theme: https://codex.buddypress.org/how-to-guides/building-a-buddypress-child-theme/

Then, you’ll want to overwrite the header.php file on line 79. Here’s the documentation for the wp_list_pages: https://codex.wordpress.org/Function_Reference/wp_list_pages the exclude parameter should work for you. If you don’t know the pages’ id, you can use this plugin: https://wordpress.org/extend/plugins/wp-show-ids/