You don't have to do anything to that account. Just stop voting for it, and vote for other people's posts.
As someone pointed out, a vote for someone else is equivalent to a downvote for the bad actor, because the reward pool is fixed and shared out via percentages.
Basically it needs the community to go on a mass voting spree for good posts, and the amount the bad posts get will automatically shrink without anyone having to do anything explicit.
Problem is that the majority of the SP holders are in circle jerk or vote for these type of accounts.