1. Open your browser and go to outlook.office.com
2. Now click in the URL bar and add /inclientstore after /mail.
3. The link should look like this: https://outlook.office.com/mail/inclientstore
4. Wait a few moments until the screen with the add-in appears.
5. Click on "My add-ins".
6. Click on the three dots next to FileCap.
7. Select remove to uninstall the add-in.
Due to Microsoft's synchronization time, it may take up to 24 hours for the add-in to be removed from Outlook.