What you need to do is make sure you have a unique base for your author permalinks. This sample code would do what you need. You may need to flush the rules after you include this code in your functions.php. A rewrite rules inspector plugin will help you get this all working smoothly:
function wpse263881_init() {
global $wp_rewrite;
$wp_rewrite->author_base="author";
$wp_rewrite->author_structure="https://wordpress.stackexchange.com/" . $wp_rewrite->author_base . '/%author%';
}
add_action('init', 'wpse263881_init');