MS Teams - Mute a Chat
Desktop:
To stop getting notifications for one of your chats, find the name of the chat and click More options 
> Mute.
Only the notifications are turned off, so you still receive messages and an icon appears next to the names of the participants to remind you that the chat has been muted.
If you change your mind, just click More options again and unmute it.
Mobile:
Go to the desktop or web app to mute a chat.