To become a lead ISO Auditor you need to have at least four years of experience in process management and Quality management , of which at least two years on a job related to information security.
To Get ISO 27001 lead auditor certification, you must attend a course and pass its final exam.
To have Ensure good prior experience.
You must Attend ISO lead auditor training program.
You Must Find a certification body Which is accepted by global benchmark and the registrar has certified should be listed on his website so you can easily find out.
I have one reference course who provides ISO 27001 lead auditor certification with training. The cost of this ISO 27001 lead auditor certification cost is reasonable. This course is made by GSDC (Global Skill Development Council).
Here is the following link where you can check out the syllabus:
https://www.gsdcouncil.org/certified-iso-27001-lead-auditor