First, admins can generate a report via the SharePoint admin center to identify any such accounts across their organization. These reports — which display information such as username, email address, account type and the date of last activity on the account –—will be widely available beginning this Friday, Aug. 16.
Once unlicensed accounts have been tracked down, they can be deleted, assigned a new license (which requires a Microsoft 365 or Office 365 subscription that includes OneDrive for the user), or kept in the Microsoft 365 Archive.