There are two ways to unhide the words or sentences you have hidden.
The first method is to:
1. Go to the "Home" tab and select the subtopic that contains the hidden word/ sentence.
2. Tap on the Vocabulary icon.
3. Reach the end of the Vocabulary of that subtopic and tap on the button that indicates the hidden units.
4. Tap the switch button to unhide the hidden units.
The second method is to:
1. Open the Search.
2. Find the word or sentence you have hidden.
3. Select that word or sentence and tap the switch button near the "Learn This Word" option.
How do I hide the words or sentences I already know?