Internal audits are an important tool for continual improvement in your Management System (QMS, EMS, et.al.).  It is critical that your internal auditors maintain and improve the skills to properly review your processes and records, to identify strengths, weaknesses, and problems in your Management System.

To ensure competence, it is important your internal auditors are properly trained.  After completing a course, they are tested and receive a certificate to show Objective Evidence of their competence.

Online Standards Training via Ingentius.com has Internal Auditor Training packages for these standards:
Be sure to use discount code: 2020ASR  for a 30% discount
(good until the end of the year)