1) Request a password reset be sent to the email address associated with your Untappd account here: https://untappd.com/account/reset_password
2) Once that is received - clicking the unique password reset link will take you to the page where you can set your new password. Here you will see, "Do you want to log-out of all devices and third-party apps?" - selecting Yes from the dropdown will logout all devices (and third party applications) that are connected to your Untappd account.
Have some questions? No worries! One of our App Support Specialists will be more than happy to help explain how to logout of all connected devices on Untappd or help troubleshoot any issues you are having with it. All you need to do is leave feedback on this article, or submit a help request here.