Deleting reminders

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I was using Google Assistant to create reminders. I also used the Assistant to delete them.

Then I got this suggestion when I opened it up to switch to Google Tasks to manage them.

Now , when I try to delete the reminders, although the Assistant responds that they have been deleted, none are deleted.

Also, on the Google Tasks page, the option to delete all "completed" task does not work.

I am somehow supposed to use some voice command to evoke the Google task manager to do this?

If not, how can I revert back to the Google Assistant?