MS Teams - Leave a Group Chat
Desktop:
To leave a group chat, go to your chat list and find the chat you want to leave. Click More options 
> Leave.
Remove someone else from a group chat
Currently, there's no way to remove someone else from a group chat. You can always start a new conversation with a different group of people, though.
iOS:
To leave a group chat, tap the chat header and then tap Leave chat.
Remove someone else from a group chat
Currently, there's no way to remove someone else from a group chat. You can always start a new conversation with a different group of people, though.
Android:
To leave a group chat, go to the chat header and tap More options 
> Chat details > Leave chat.
Remove someone else from a group chat
Currently, there's no way to remove someone else from a group chat. You can always start a new conversation with a different group of people, though.