This article covers the user experience on Mac computers
FileVault Key Regeneration
Any Mac that enrolls into Iru that previously had FileVault enabled will automatically prompt you to regenerate your FileVault Key so it can be escrowed.
Authenticate
You will be prompted to authenticate with your FileVault Credentials, as shown below. Authentication and user interaction are required due to how FileVault works.

Related Articles
Configure FileVault
Enable FileVault and escrow the recovery key that this prompt regenerates.
Report FileVault keys escrowed to iCloud
Alert when a FileVault recovery key is stored in iCloud instead of with your organization.