In some circumstances it is useful to upgrade an existing meeting to have Teams functionality.  You can easily do this without having to delete the meeting and create a new one.

Only the original creator of the meeting can upgrade it to a teams meeting.

Using the Full version of Outlook

Step 1 - Open the existing meeting in outlook.

Step 2 - Click on the Teams Meeting option in the top bar.

Step 3 - Click Save and Close

Using the web based version of Outlook

Step 1 - Edit the existing meeting in the outlook online calendar.  https://outlook.office365.com/calendar/

Step 2 - Click on Add online meeting under the Rooms and Locations and click Teams Meeting

Step 3 - Click Save