The easiest way to change the Share My Cook account registered to the device is to use the BBQ Guru app menu to Logout From ShareMyCook.
After logging out, go back to the main app menu and select Connect to WiFi.
Follow the prompt to either enter different ShareMyCook account credentials or to create a new account. Once completed, re-establish your WiFi connection by selecting your network and entering the password. Your device will now be active on the new ShareMyCook account.