They are not a comrade. They're a liberal who wants some welfare capitalism most likely but they're not a comrade if they're saying those things and like the horse-dong enthusiast streamer pedo.

Basically this person sounds like a social fascist to me. So approach them appropriately (rather than thinking them merely wayward but a communist as your post suggests which is emphatically false and must be rejected to understand where they are) understand what they are and understand you're probably wasting your time compared to just talking to someone who isn't a terminally online weirdo caught in a CIA streamer's parasocial cult.

The well has already been poisoned for you so you have quite a bit of work if they're deranged enough to call you a tankie. If you choose to work on them it's going to take a lot of time, you'll need good research skills, good debunking skills, and a lot of patience. No one is going to be able to hold your hand month after month and feed you points to rebut theirs and to educate them, this is a skill set you must have or be willing to develop or you should abandon this venture now. You should also understand it could easily take a year of unremitting replies, research, and so on to get anywhere and you could end up spending 8 months only for them to block you or otherwise shut it all down. They don't seem like someone who will act in good faith, they have a preferred understanding of the world, a position in it (labor aristocracy of the imperial core) that is materially advantaged by rejecting your views and doubling down on support for empire.

You'll have to send them info, be ready for it to be rejected, often out of hand without any real rebuttal other than "unreliable source because any reliable source would condemn the commies". So part of your research should try and go for at least semi-neutral seeming (to them) sources for some things where possible. I would suggest trying to undermine the US and capitalist system instead, highlight the atrocities, the flaws, the lies, the propaganda, the false flags, the influence operations, the history of abuse of the working classes, the history of empowering and elevating reactionary including socially reactionary elements, and so on. I would begin with at least dragging their side down, bloodying the bourgeois media they like as untrustworthy or at least deeply compromised at many points and times and then pivoting to underscoring how the Soviet Union had real gains for its citizens, its pitfalls, the problems it faced including most of all the capitalist west attacks on it resulting in siege socialism.

Oh I'd also absolutely hammer them on their favorite streamer pedo with CIA characteristics with all the dirt on him as a first thing. If they don't budge at all on that and supporting him/watching him/trusting him I'd say give it up until they do.