You can't. According to the survey of Happy Crew, after the four certificates of crew expire, they need to go to a professional school recognized by the Maritime Safety Administration for study and training (commonly known as make-up exam training). After passing the examination, the maritime agency will issue a new certificate and will not go to work on weekends and holidays. So you can't change the crew's four certificates on weekends. The four certificates of crew include: familiarity and basic safety training certificate; Proficient in survival craft and rescue boat training certificate; Advanced fire protection training certificate; Proficient in first aid training certificate; Advanced medical training certificate.