Before beginning a complete uninstall be aware this should only be done if you tried re-installing the app and restarting the computer as you will loose a few of your preferences and defaults and will need to login again.
Below is the link to re-download teams so you can reinstall then restart and see if it works, if it doesn't then go to step 2.
Step 2
Open your Application Folder on your Mac, and select the Microsoft Teams app and drag it to the Trash.
1) Click Go > Go To Folder
2) Then paste each of the paths below one by one into the field and delete the files in that folder - repeat this process for each of the line items. IF nothing shows up in that folder move on to the next you will be doing this 11 times until all the teams files have been deleted.
If teams is open you will need to quit the Microsoft Teams app - If you can't, go to the go menu and select the utilities then open activity monitor select Microsoft teams and select the X in the upper left