How to make company auditor?

To become an organization that can certify other organizations against an ISO standard, like ISO 27001, the organization needs to undergo an accreditation process performed by an accreditation body against ISO/IEC 17065. In general, each country has one accreditation body (e.g., UKAS for the UK, or ANAB for the USA).

Considering that, you need to contact the accreditation body from the country you want to become a certification body and ask for the details of its accreditation process.

You can have an overview of ISO/IEC 17065standard here: https://www.iso.org/obp/ui/#iso:std:iso-iec:17065:ed-1:v1:en