If payment has not been made, the booking is automatically canceled after the payment deadline, which is specified in the email with your order details. If you want to make a new booking for a flight with the same airline or simply free up booked seats for other passengers, you can contact the Care Service chat and provide the operator with the order number that needs to be canceled. 

You can find the chat on the website in the bottom right corner of the screen:

In the app, the chat is located in the bottom center block:

Please note that these conditions apply specifically to orders for which an airline ticket has not been issued.