Answered: how to remove given votes to a question or answer?

As far as I know, there is no plugin to do this automatically. However, there are a couple of options.

Option A:

 1. Remove the votes from the database directly

 2. Recalculate points and recount posts (it's not a must but it is better to do so)

Option B:

 1. Delete the user. I know it might sound as too much but many times these users are spammers and you might want to delete those users anyway