Call file / class from ThirdParty folder

That's the correct way to call it, so you probably don't have it loaded. Read up on autoloading if you'd like the framework to handle it for you:
https://codeigniter4.github.io/userguide...oader.html

For example, if you wanted to use your code above, app/Config/Autoload.php might look like this:

PHP Code:

$psr4 = [
    'Config'      => APPPATH . 'Config',
    APP_NAMESPACE => APPPATH,                // For custom namespace
    'App'         => APPPATH,                // To ensure filters, etc still found,
    'TP\Tools'    => APPPATH . 'ThirdParty/TpTools',
]; 


(You might want to use the classmap instead, depending on what the library looks like.)