First, attend the ISO9000 external auditor training course, and obtain the training certificate issued by the training institution after passing the examination. Then take the exam arranged by CCAA with ID card and training certificate, and pass the exam (70 points) to obtain the qualification of registered auditor. There are certain conditions for applying to become a registered auditor, including two years of undergraduate graduation and four years of work. Different systems have different requirements.
Details can be found on the website of China Certification and Accreditation Administration. Or call the training institution for consultation, and they will have information about the start time of the training course for external auditors.