If you are not able to find the Teams meeting button in your Outlook desktop app, then it most likely mean the Add-ins are not registered. You can check under Outlook Options
The location of the DLL are in the following folders, each for x64 and x86. Version number may be different depending on the version of Teams app you have installed.
If you tried adding them without success (which means it does not appear in the list), it means it is a permission issue. Copy the following and save it as .bat file and run it. If you get Access Denied error, then, you need to run it as as admin