workflow automates to setup primary contact

Hi, I have mapped data into account and contacts, but the primary contact doesn't display in the primary contact field. I am trying to update through out of box workflow. One of the fields in contact is bit value, 1 or 0 , 1 means primary, then, how can I set this condition in workflow. I have associated contacts with account, and trying to update the parental account primary contact field once one associated contact created or changed.