Once you are done working with a device, you can end the session or release the device completely.
Since version 11.8 - simply closing the browser tab will end your session and release the device automatically.
Releasing a device from within the device reflection screen
Click on the red End button to end the session. In the popup, click "Release" to release the device reservation.
If you wish to end the session but keep the device reservation, click on "Keep Device"
Releasing a device from the device grid view
In the grid view, locate the device that you have previously reserved. You can identify devices that you have reserved by looking for your email. Once you have located the device in question, click on "Release".
Then, in the popup click on "Cleanup and Release":