function is_ios_device() {
    return preg_match('/iPhone|iPod|iPad/', $_SERVER['HTTP_USER_AGENT']);
}

function is_android_device() {
    return preg_match('/android/i', $_SERVER['HTTP_USER_AGENT']);
}

function redirect_if_desktop() {
    if (!is_ios_device() && !is_android_device() && is_page(XXX) && !is_user_logged_in()) {
        wp_redirect(home_url());
        exit;
    }
}
add_action('template_redirect', 'redirect_if_desktop');

function redirect_if_ios_mobile() {
    if (is_ios_device() && is_page(XXX) && !is_user_logged_in()) {
        wp_redirect('https://apps.apple.com/......');
        exit;
    }
}
add_action('template_redirect', 'redirect_if_ios_mobile');

function redirect_if_android_devices() {
    if (is_android_device() && is_page(XXX) && !is_user_logged_in()) {
        wp_redirect('https://play.google.com/store/.....');
        exit;
    }
}
add_action('template_redirect', 'redirect_if_android_devices');