How to add/enable Teams Meeting option in Outlook

Open your Microsoft Outlook app.
Once opened, on your settings options choose File. 

On your left pane, choose Options.

After that, it will pop up setting in Options. Choose Add-ins.

Once clicked, you may see it as per below.

Click on the "Microsoft Teams Meeting Add-ins for Microsoft Office" and click the button Go... as per the image below.

Once clicked, it will show as per below. You need to tick the one same as a yellow highlighted option and click the button OK.

It will automatically enable your Microsoft Teams Meeting as per below.