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.
Login to the Microsoft 365 admin center.
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
For the old admin center: Click OneDrive Settings and click Initiate next to Sign-Out
For the new admin center: click Initiate Sign-out