You can quit Teams completely to resolve issues you may be experiencing with Teams i.e. messages not sending, chats not updating.
Simply locate Teams on the notification area at the bottom right of your screen:
Right-click on the Teams icon and select Quit.
This will close Teams completely. If you close Teams using the X at the top right of the Teams window, it still runs in the background to ensure you can receive messages.
Simply re-open Teams by double-clicking on the Teams icon on your Desktop and you will be signed back into Teams.