Rule source on GitHub

DowngradeTypedPropertyRector

Changes property type definition from type definitions to @var annotations.

 class SomeClass
 {
-    private string $property;
+    /**
+     * @var string
+     */
+    private $property;
 }

Configure your rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\DowngradePhp74\Rector\Property\DowngradeTypedPropertyRector;

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