Well, if you look at the comment you're replying to it's already telling you something concrete you can do beyond merely feeling bad: namely, being sympathetic to people of colour when they say things like "I'm done with white people" out of frustration, and not (for instance) immediately holding this up as proof that PoC are just as racist and so shouldn't complain. You may not like the idea of doing that, but it's definitely a concrete action.

I think listening does a bit of good. Understanding does even more, and sharing that understanding so they don't have to does even more good. The unfortunate fact is that you'll be listened to better by another white person than a person of color, who'll be perceived as being "biased".