Configure your rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\Transform\Rector\StaticCall\StaticCallToFuncCallRector;
use Rector\Transform\ValueObject\StaticCallToFuncCall;

return RectorConfig::configure()
    ->withConfiguredRule(StaticCallToFuncCallRector::class, [
        new StaticCallToFuncCall('OldClass', 'oldMethod', 'new_function'),
    ]);