We assign a random ID to a device or interface when the request is sent from an Orion web page to a Toolset tool. The same ID is sent for subsequent requests for that same device or interface. Once you enter credential information for that ID on the Toolset side the map between ID and credential is stored local to the Toolset host machine. This is to protect the credentials from being passed and to prevent the user from having to enter fresh credential information for each request.
To clear the credential information right click on the same device or interface you initiated the request from to see the integration menu. Then select 'Settings' from the menu. You should see a "Settings" dialog that had tabs for "Community Strings", "SNMPv3 Credentials", "Menu Items", and "Automatic Menu Items". Select the community string or SNMPv3 tab and you can clear all credentials or select a single credential and clear it. Then next time that device or interface ID is sent you will be prompted for credentials again.
One potential complication is depending upon what is going on in your browser at that time the browser may refresh on top of the Settings dialog. So if you don't see the Settings dialog look behind your browser.