There isn't a way to tell a Nazi they are wrong without challenging their beleifs.
There isn't going to be a "nice way" to convert fascists into reasonable people.
If they cared about other human beings, OR cared about understanding the world around them, they wouldn't have fallen down this easily avoidable pitfall. And there isn't a good way to get the ignorant to seek information.
If you try to be their friend or just non-hostile it will always be read as validation of their beleif system. And that is unacceptable