Configure your rector.php:

<?php

use PHPStan\Type\StringType;
use Rector\Config\RectorConfig;
use Rector\TypeDeclaration\Rector\FunctionLike\AddParamTypeForFunctionLikeWithinCallLikeArgDeclarationRector;
use Rector\TypeDeclaration\ValueObject\AddParamTypeForFunctionLikeWithinCallLikeArgDeclaration;

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