It is not always immediately productive to debate low-key white supremacists. Do not expect to see quick results.
But the most effective thing you can do is force them to confront what it is that they actually believe, and why.
Well, the thing with right-wing ideologies is that they work largely by making people believe something without actually realising it, and using a lot of deceptive language to do it.
"I don't hate black people, I just dislike black culture."
Well, what do they mean by black culture? What elements are disliked? Why do they dislike those elements? Why is that a valid justification?
What do they actually think capitalism is? Who gets to define what is and isn't "natural?" How are they defining it?
And they don't fully understand the things they're saying because there's a problem with their beliefs.
The idea of having an "inferior culture" has been used as an excuse for racism for millennia.
Ask them what they truly mean.
Nobody can honestly claimed to be SHOCKED to learn the n-word is offensive.
But they might not actually understand why that is.
Because sometimes they really don't.
"Why are people so afraid of the truth? Why are they so afraid of frank discussion?"
It's because beliefs have real-life consequences.
Less brown people voting? Doesn't matter, intent was to decrease illegal voting, so not racist.
However, forcing a person to confront what it is that they actually believe? It's, at the very least, much easier.