Your account is protected by the passcode which is needed to open an application. To block the device you can contact our customer support and inform us you have lost your phone, or it got stolen, and we can block access from mentioned device.
To do that we need from you: device type and operating system.
After we block your device, you must log in on another smartphone and unpair the stolen or lost device from the application. In order to unpair your phone you need to click on the person icon in top right section of the dashboard, select "Settings" -> "Security"-> "Unpair phone".