Any trained auditor should be able to do it, but not the person overseeing the audit process. And auditor should focus on audit records, etc. in which s/he did not participate.
Auditing is no different ... read the audit section of the standard, read the internal audit procedure, develop a list of questions, and interview & check records until those questions are answered.
If for some reason you are concerned about independence, objectivity, etc. then contract with an external person to audit that portion of the system, or find another local company audit audit each others audit processes.