Due to the integration with Speedgrader, there is no way to integrate an existing Flipgrid Topic within Canvas. If you want to use Disco Library Topics or old Flipgrid Topics, you would need to use Flipgrid outside of Canvas.

Instead, each time you create a new Canvas assignment and select Flipgrid as the external submission type, it will automatically create a new Flipgrid Topic. Then, you can edit the details of the Flipgrid Topic.

If you plan to duplicate Topics in the future, include all assignment details within the Canvas assignment and then Flipgrid can simply be where students submit their video. That way, all assignment details would be copied over for future courses.