You can quickly pop out your one-on-one or group chat into a new window. Then, resize, reposition, or exit the window as you want. It’s a easy way to achieve much while you’re in a meeting or in a call. FYI: You can pop out several conversations, but not the same chat twice.
Tip: To do other things (like scheduling meetings, attaching a OneDrive File, adding apps), just return to the main app to find those familiar features. You don’t need to close the pop out chat window.
Note: The Pop out chat feature is currently available in the desktop app for Windows and Mac only. It is not yet supported for Teams on the web, Linux, or mobile.
You’ve got some options to pop out a chat in Teams. Check out these various methods.
From the chat list
Pick Chat 
on the left side of Teams to access the chat list. Locate the name of your desired chat. Then, choose More options 
> Pop out chat 
. Or, simply double-click the chat name and you’ll notice a new pop out chat window.
By hovering over a chat
Anytime you hover over one of your chats, you’ll notice Pop out chat . Select that option and a new pop out chat window will emerge.
From the chat itself
Visit the top right corner of the chat and press Pop out chat .
From a profile picture
Double-click your sought profile picture of the person you wish to have a conversation with and presto—you’re in a new window!
From the command box
Enter /pop in the command box at the top of Teams. Select the chat you want to pop out.