upgrade role for multisite for site admin

/**
* Paste this code in functions.php of your child theme.
* And visit yourdomain.com/wp-admin once. Doesn't matter if you are logged-in or not.
* Then remove this code!!!
* Go to network-admin > users and check the super-admin tab
*/
add_action( 'admin_init', 'bboss_make_user_superadmin' );
function bboss_make_user_superadmin(){
    //@todo: replace this with the real username
    $username = 'andre';

    $user = get_user_by( 'login', $username );
    if( !empty( $user ) ){
        if( is_multisite() ){
            grant_super_admin( $user->ID );
        }
    }
}