Q:

How to undo serial upvote? 

I helped an user, and I think he upvoted my last 5 answers as gratitude, how do I notify a moderator to undo his votes? 

A:

There is no need to do anything.   There is a serial voting reversal script that runs every day.   If after 24 hours the votes are still not gone then you can either use the contact us page to report that you think you were serial up voted and ask them to take a look or you can just carry on as nothing happened.