Sign a User out of all Office 365 Apps and Sessions

If you need to remove a users access to an account immediately, the steps below will force a sign-out on all devices signed into with the account.

We highly  recommend blocking a users sign-in  and  reset their password first.
  1. Login to the Microsoft 365 admin center.

  1. In the Microsoft 365 admin center, select Users > Active Users > Click on the users Display name you want to sign out of apps and sessions

  2. Click OneDrive Settings and click Initiate next to Sign-Out

Resources:

https://docs.microsoft.com/en-us/office365/admin/add-users/remove-former-employee?view=o365-worldwide#block-a-former-employees-access-to-office-365-data