You can restart a topic by scrolling down in the Word Preview list, and clicking on the Restart topic button. Find the Word Preview list by clicking on the arrow pointing up in the bottom left corner of the topic.
1. To open the Word Preview list, click on the up arrow in the bottom left corner after a word is introduced.
2. Scroll down to the bottom of the Word Preview screen to find the Restart topic button.
Also, you can delete your entire progress by deleting the app and installing it again. This only works if you have not yet synced your progress (in other words, you have not logged in to Drops using your email, Facebook or Google).