Sorry for our late reply. We have no datasource for existed PDO so you can create one like this:

1- Create a ExistedPdoDataSource.php with following content:

class ExistedPdoDataSource extends \koolreport\datasources\PdoDataSource
{
    protected function onInit()
    {
        $this->connection = Utility::get($this->params,"pdo");
    }
}

2- In your report, you can use the above datasource like this:

require_once "ExistedPdoDataSource.php";

class MyReport extends \koolreport\KoolReport
{
    function settings()
    {
        return array(
            "dataSources"=>array(
                "class"=>ExistedPdoDataSource::class,
                "pdo"=>$this->params["pdo"]
            )
        );
    }
    ...
}

3 - To render report, you do this

require_once "/path/to/koolreport/core/autoload.php";
require_once "MyReport.php";

$report = new MyReport(array(
    "pdo"=>$conn
));
$report->run()->render();

Hope that helps.