Do you want to do this for one user or for all users? For just one user, admins and supermods (i think supermods can) can do this on the users profile page. It would usually be on the right of the main table header (the one with 'send message' dropdown, usernotes ,etc).
If you happen to use Cybernetic's "Advanced Rules" mod, it has an option to reset the rules for everybody. I'm not sure if vbulletin does that natively or not because I've always used that Cyb plug. If not, maybe it could be done with an sql query? Not sure.