How to access 3rd party report?

You're correct in leveraging AWS Artifact for an auditor's request.

Third-party reports are available under certain circumstances to customers that have been granted access within AWS Marketplace Vendor Insights:

• Third-Party Reports
• Vendor Insights

1.) AWS Artifact Agreements are typically only required for additional operating requirements like HIPAA and not necessary for generating SOC reports.

• Managing Agreements

2.) You can download the SOC I report from the AWS Reports tab and searching for SOC.