Additional election officials shall report to the election board at the polls at the time designated by the election supervisor or the chairperson of the election board to assume their duties to assist the election board in counting the vote. Before undertaking the duties of office, each additional election official shall subscribe to an oath to honestly, faithfully, impartially, and promptly carry out the duties of the position. If an additional election official fails to appear and subscribe to the oath at the time designated by the election supervisor, the election board shall appoint any qualified voter to fill the vacancy.