Amy is an Org Owner on an Enterprise Grid plan.

Using an integrated Data Loss Prevention (DLP) solution, delete the file, and then review the Audit Logs API to see who downloaded the file.

Using MDM, disable file downloads and then use session management to see who was logged in and downloaded the file.

Using a third-party eDiscovery app, delete the file and use data exports to determine who downloaded the file.

Using Slack Enterprise Key Management (EKM), revoke key access for the file, and review the EKM logs to see who downloaded the file.