If you lose your EasyCard or iPASS while renting YouBike, you should promptly contact the electronic ticketing company or submit a loss report through their official
website. After completing the loss report, the balance on the card will be protected.
Additionally, YouBike members can protect their rights by calling the YouBike customer service center. The YouBike staff will verify the identity of the renter to confirm that they are the registered member of the lost card. After checking the system to ensure the bike has been returned, the staff will assist the renter in deactivating the card number to prevent it from being used by other YouBike users.
Source: Department of Transportation, Taipei City Government