I had kind of weird situation few days ago, when Teams meeting add-in in Outlook just disappeared for no visible reason. Not having that add-in in Outlook actually prevents you from scheduling Teams meeting from Outlook, which not a nice situation. You surely can do it directly from Teams calendar, but that might not be so convenient for several reasons. I first tried some common and known troubleshooting steps. I restarted Teams app, as well as Outlook, tried to reinstall Teams, but nothing helped. The only option was to reinstall Office apps, but I was not in the mood for that for several reasons, so I decided to dig deeper into this issue. On another computer, where Teams meeting add-in was present and working, I opened Outlook, switch to Options and opened Add-ins console. There, I was able to locate Teams meeting files location, like you can see on the following screenshot:
As you can see, it is located in within AppData folder in your user profile. AppData folder is hidden by deafult, so you need to set folder options to actually see it.
When you browse to the folder where Teams meeting add-in is located you can find install log file. It is called meeting-addin-install-logs. When you open it, you can see what was going on with this add-in. However, you can also find a command that is being executed for Teams add-in installation.
This command is:
regsvr32.exe /s /n /i:user "C:\Users\userprofilename\AppData\Local\Microsoft\TeamsMeetingAddin\1.0.20077.4\x64\Microsoft.Teams.AddinLoader.dll"
So, I closed the Outlook and I ran command prompt with elevated privileges, and executed this command. After I got command prompt back again, I restarted the Outlook and – Teams add-in was there again 
.
Take care!
.