This post showing you of one the possibility to pull out the Teams Meeting icon in Outlook Appointment. In the proper Outlook Appointment screen you should see Teams Meeting while you are in Office 365 environment.
If you do not see the above icon then try to do the following. Sign in to your Skype for Business. Click the Try it in the purple color bar.
Login to your Microsoft Teams, download it if you do not have one. Then reopen your Outlook you should have the icon.