In the western world there is no stronger programming that is instilled into us than the 'muh holocaust' narrative. If he's on the road to being red-pilled just give him more time to 'notice' things that don't make sense. It took me a while to get there. I know of many people like him that claim to be red-pilled but haven't yet accepted that different races have different natures, that history is written by the victors, and that WW2 was a failed slave revolt.