Class is Not Found After Upgrading codeigniter 4.0.x to 4.1.x

Currently i'm on codeigniter 4.1.9. I have a class in library and call it in controller. In previous Codeigniter 4.0.x, it works fine. But after upgrading Codeigniter to 4.1.9 there is error class not found.

Here is the code:

Code:

Use Export_csv;
$class = new Export_csv;

I upgrade the Codeigniter by downloading the rar from ci4, copy folder controller, library, model, and view to folder gplay app.

Big thanks for your help