The ability to toggle and switch back to Classic Teams from New Teams will remain an option for a limited period of time.  Follow these quick steps to determine if you are currently using New Teams and then if desired, revert back to Classic Teams on your Windows or Mac device.

With Microsoft Teams open, locate the top left corner of Teams and check if the Teams logo appears with "New"

After confirming you are using New Teams, in order to switch back to Classic Teams locate the "..." icon next to your Teams picture or User Icon

In the drop-down menu that appears click on the toggle labeled "New Teams"

Once this toggle is selected New Teams will close and Classic Teams will open