You should get into the habit of logging out when you have finished your session - here's how
To log off when on the main start screen, click the logout button, top left
Most of the screens in Flow360 also have a logout button near the bottom of the lefthand side bar. Simply click to immediately end your session and logout.
When you log a new Helpdesk issue you have the option of saving the issue and logging out all in one go by using the Confirm & Logout button, top right.