If you e-filed already, you need to file an amended return. There is no extra cost, but you should wait until your first tax return is processed and the refund is paid.
If you paid the fee but did not file, you should be able to make changes before going back to the File step, and you will not be charged again. If you need to "clear and start over" after paying you must call customer support.
https://ttlc.intuit.com/community/using-turbotax/help/what-is-the-turbotax-phone-number/00/25632
