On the left side of your browser's session window, you should see a tab which you can click to expand the web client options:
![side tab of session window](https://teamdynamix.umich.edu/TDPortal/Images/Viewer?fileName=964199a8-5ba9-4b33-9b16-6f1c2928e56a.png)
You can then lock or unlock your session by then clicking the button at the top-left to Send Ctrl+Alt+Delete to current work area:
![lock/unlock session option](https://teamdynamix.umich.edu/TDPortal/Images/Viewer?fileName=37db8045-a082-4d02-87af-23c7d95b6772.png)