First is important to note that an ISO 27001 auditor or implementer is not accredited, but certified.
Additionally, certifications can be issued only by certification bodies, not persons, and to work for them you need to be a certified auditor.
Considering that, to start your journey to become an information security auditor you should attend an ISO 27001 Lead Auditor Course, so you can understand the concepts of the ISO 27001 management system and the processes and techniques involved in an audit.
After attending the course and be approved in the exam, if you want to work as a certification auditor, you need to accumulate audit hours working for a certification body, first as an observer, and after that as an audit team member, so you can gain understanding and experience in practical audits. After sufficient auditing hours for a certification body, and good evaluations from your team leader, you can achieve the status of certification auditor and after that certification for lead auditor.
To become an ISO 27001 implementer, you do not need to be certified, but an ISO 27001 implementer certification can be a competitive differential. To become an information security implementer, you should attend an ISO 27001 Lead Implementer Course, so you can understand the concepts of the ISO 27001 management system and the processes and techniques involved in implementation. After attending the course you need to take an exam and be approved.
These articles will provide you a further explanation about Iso 27001 implementer:
Please note that organizations that issue certifications are certification bodies. An accreditation body is another type of organization, the organization which authorizes organizations to act as certification bodies.
Considering that, to certify an organization your company has to be accredited by an accreditation body (e.g., UKAS for the UK, or ANAB for the USA), and for this purpose, your organization has to be certified by an accreditation body against ISO/IEC 17065. You can have an overview of this standard here: https://www.iso.org/obp/ui/#iso:std:iso-iec:17065:ed-1:v1:en
This article will provide you a further explanation about accreditation and certification: