Not more than thirty days before each primary or general election, the board of voter registration and elections or other electoral board must instruct the managers and clerks appointed to serve in the election in the use of the machine and their duties in connection therewith; and the board of voter registration and elections shall not permit a person to serve as a manager or clerk, if there are clerks, who is not fully qualified to conduct an election with the machine. However, nothing in this section may be construed to prevent the appointment of a person as a manager or clerk of election to fill a vacancy in an emergency.