[PnP-Focus] ISO Lead Auditor Training

Can someone enlighten me on the step-by-step procedure for becoming ISO
Lead Auditor? 
 
I understand that even after the 5 days course one should work without
any remuneration along with a senior Lead Auditor for 20 days or so to
become qualified to be a Lead Auditor. I understand that even for this
20 days training one has to sometimes wait for months or one can
complete this OJT after months only because of the long queue of those
who have completed the Lead Auditor Training course but who are yet to
go through OJT (ON THE-JOB-TRAINING). 
 
I am terribly confused.
 
Thanks in advance for the clarifications.