Rule source on GitHub

DowngradeDeprecatedAttributeRector

Downgrade #[\Deprecated] attribute to @deprecated annotation

 class SomeClass
 {
-    #[\Deprecated(message: 'use SomeOtherMethod() instead', since: '1.5')]
+    /**
+     * @deprecated 1.5 use SomeOtherMethod() instead
+     */
     public function someMethod(): void
     {
     }
 }

Configure your rector.php:

<?php

use Rector\Config\RectorConfig;
use Rector\DowngradePhp84\Rector\ClassMethod\DowngradeDeprecatedAttributeRector;

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