class SomeClass
 {
-    public function process($name)
+    public function process(string $name)
     {
     }
 }

Configure your rector.php:

<?php

use PHPStan\Type\StringType;
use Rector\Config\RectorConfig;
use Rector\TypeDeclaration\Rector\ClassMethod\AddParamTypeDeclarationRector;
use Rector\TypeDeclaration\ValueObject\AddParamTypeDeclaration;

return RectorConfig::configure()
    ->withConfiguredRule(AddParamTypeDeclarationRector::class, [
        new AddParamTypeDeclaration('SomeClass', 'process', 0, new StringType()),
    ]);

SETS:  phpunit/phpunit 8.0 symfony/* 5.0 symfony/* 5.1 symfony/* 5.2 symfony/* 5.3 symfony/* 6.0 doctrine/orm 2.5