Is that screenshot from a poll? 🤨
But yeah, to stop that kind of cheating you could use my plugin to stop new accounts from voting in polls made before they registered. And I see you actually have already posted there (and I've replied, too).
As for deleting the current votes, I believe the software used to have a way to change the votes (back in 2.x or 3.x I think?) but it looks like there's nothing like that in 4.x so it must have been removed at some point. Until IPS add back such function your only solution would be to have a custom modification done.
Or, a simpler workaround would be to ban/delete those accounts, install my plugin linked above (if you haven't already), and re-create the poll so voting starts from scratch.