Go back to the Samsung Members landing page (this app), and at the very bottom of the screen, you should see GET HELP. Click this, then click on the 3 dots (top, right), then SETTINGS. At the top of this page, you will see SAMSUNG ACCOUNT - click on this, then open DEVICES. Apart from the device you are using, you will see a list of other devices that are logged in to your Samsung account - click on the 3 dots of the "rogue" devices, then click SIGN OUT.
