How to re-enable the Teams add-in on Outlook

Open Outlook and click on File in the top-left menu.

Click Options at the bottom of the left sidebar.

In the pop-up window, select Add-ins from the left navigation panel. Click Manage, select Disabled Items from the dropdown and click Go...

Select Microsoft Teams Meeting Add-in for Microsoft Office, click Enable, and then click Close.

Click OK to close Options, then restart Outlook.