Ordinarily, I go and make a playlist with the affected videos, then ask my subs/friends to like all of them if they haven't already. I'd chose a core of people I talk to generally and see if they'd help out.
I've run into this before, actually, early on when I first got a YouTube channel to talk about the anthropology of Mill Ave, I ran into a votebot. By this I mean, I ran into someone who felt the need to put 30 dislikes on every video I had at the time overnight. Frankly, I wish that YT at the time had a method for getting all of them removed; because I think there would have been an obvious sign of malicious behavior there--after all, if 30 dislikes happen on all my videos in less than a few minutes.