After you play a round of Moved or Endless, scroll right until you come upon the power-ups menu, which should include buttons for Shrinkers, Time Stops, and Expanders. Just below the list of power-ups, click on the "Dot Doubler/Learn More" button.
On the subsequent menu, click "Restore" in the bottom right corner.
If this doesn't work, e-mail us at help@weplaydots.com.