Below are the two ways to navigate & open an existing Quiz/Test:
From AI Tools Tab:
Click on the "AI Tools" tab on the left side menu:
The Tools page is displayed.
Click on the Quizzes & Tests Tile:
The Quizzes and Tests page is displayed.
You can open an existing Quiz or Test, from the list of Past Outputs shown on the right hand side, by clicking on the preview.
From the My Resources Tab: