Signing in and out of call queues (sometimes also named call groups) in Teams i very easy. And you can do it from both the Teams application on your computer and from the Teams app on your phone.
In the Teams application on your computer
Go to your profile in the right corner of the Teams application and click Settings.
Then click Calls.
At the bottom you can see the call queues that you are part of. And also sign in and out of them.
In the Teams app on your phone
In the app, signing in and out also takes place inside Settings - whether you're on an Android or an Apple phone.
Click on the three bars in the upper-left corner of the app.
Click Settings and then Dial.