Well, how is it done today? Twitter is instructive. You have mostly-automated accounts that like, retweet and reply to content from a specific perspective. Often it is an incendiary perspective, and usually it's a perspective underrepresented in regular news, because that's more useful for getting people to hit like and follow on the account's post.
Once the account has gained enough real followers, they can carefully start to push payload content, the content the operator really cares about.
This drives polarisation. There's this idea that sinister foreign adversaries are trying to "spread chaos", but I don't buy it. I think it's merely a by-product of building an audience. Russia (to pick an example) doesn't care about BLM, anti-BLM, US culture wars or the Assange case. Rather, it cares about exactly the things you'd expect it to care about: sanctions, conflicts it is involved in, allies etc.
(For that matter, ad-driven media does much the same. Gawker before its demise had really gone all-in on "outrage bait" stories.)
They're going to start with the most credulous, maybe, but they'll build confidence in the same way as everyone else who's an unknown at start.