There will be times when your CRM for Outlook App might have disappeared or is not behaving as expected for a specific user. If this is the case, the user who is experiencing the issue can re-install the Microsoft Dynamics 365 App for Outlook by following the steps below:
From your CRM, click the Gear icon, then Advanced Settings
Click the Gear icon and click Apps for Dynamics 365
Scroll down to the bottom of the screen and click Re-Add the App. Pushing the app to your user account will take a few minutes to complete; once completed, you should see the Dynamics 365 App loaded in your Outlook.