How to unlink an account from Google Assistant's Action
Google Assistant has more over 1 million actions for users to use without any setup or linking. However, there are some 3rd party actions that require the users to link their 3rd party account with the Google Assistant to be working, such as smart home related actions (Arlo, Ring, etc.).
To link the 3rd party account with Google Assistant is very easy, but to unlink that 3rd party account from its action is harder because the unintuitive user-interface. To make the problem worse, Google doesn't have a clear documentation for the users to unlink their 3rd party account from the action either.
If you want to unlink the account from the action on Google Assistant, please follow the following steps:
Open Google Assistant application and go to the "Explore Actions" screen
Search for the action you want to remove the 3rd party account
On that action screen, scroll down to the "Account linking" section
Click on the "UNLINK" button on the right of that section as circled in the screenshot below
Your 3rd party account will then be unlinked from that action.