Iowa Code § 173.7: Vacancies.

If, after the adjournment of the convention, a vacancy occurs in the office of any member of the board elected by the convention the board shall fill the vacancy by election. The elected member shall qualify at once and serve until noon of the day following the adjournment of the next convention. If, by that time, the member elected by the board will not have completed the full term for which the member’s predecessor was elected, the convention shall elect a member to serve for the unexpired portion of the term. The member elected by the convention shall qualify at the same time as other members elected by the convention.