BOSTON — A new audit finds that a Massachusetts Registry of Motor Vehicles employee missed an opportunity to revoke the license of the driver accused in a crash that killed seven motorcyclists because he did not know how to add convictions to driving records. The finding was revealed Friday in a preliminary report examining why Massachusetts failed to sanction Volodymyr Zhukovskyy after being notified of his May drunken driving arrest in Connecticut. A firm hired to investigate found that an RMV employee briefly reviewed the notification from Connecticut but did not change Zhukovskyy’s record.