how to prevent an ex-employee with access from signing into QB?

Hi there, @Madhunika.

You can delete the user that is no longer working for your company. This way, their access will be removed from the company file.

Here's how to delete a user:

1. Sign in to your QuickBooks Online (QBO) account as an admin.
2. Click the Gear icon, then select Manage users.
3. Find the user you want to delete and click the drop-down in the Action column, then select Delete.
4. Click Delete again to confirm.

I'm adding this article to learn more about managing users in QBO: Add and manage users in QuickBooks Online.

You may also want to keep track of your user's activities in QBO. You can run the Audit Log report to see who made changes to your books and what they did.

Our Community forum is always open to help you again if you need more assistance managing users. Have a great day ahead!