Rule source on GitHub

DowngradeNamedArgumentRector

Remove named argument

 class SomeClass
 {
     public function run()
     {
-        $this->execute(b: 100);
+        $this->execute(null, 100);
     }

     private function execute($a = null, $b = null)
     {
     }
 }

Configure your rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\DowngradePhp80\Rector\MethodCall\DowngradeNamedArgumentRector;

return RectorConfig::configure()
    ->withRules([
        DowngradeNamedArgumentRector::class,
    ]);