You can try to use the global administrator account to sign in to Microsoft Entra admin center (This can be accessed from admin.microsoft.com-choose Identity on the left panel).
After you enter the Microsoft Entra, please choose the Application on the left pane and choose Enterprise application and use Read as keyword to search, then there is an app called "Read Meeting Navigator" and you need to choose the property of it and disable the user sign in option then go to users and groups then remove the users that registered this app.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.