Yes, you can reset answers at any point in the Lesson that you started or completed. To do so, access the Lesson and click/tap on the “Speaking Goal” button (the Home icon on mobile).
Then click/tap on Reset Answers (or the reset icon on mobile) as shown below.
Confirm if you want to reset the answers.
Note: if you reset the answers in a Lesson you completed fully, it will still preserve the completion status for this Lesson in (1) your Course completion % on the My Progress page and (2) the course progress bar on the Course tile of the Home and Courses pages.