Changing the Billing Information in the new Rakuten TV app is very easy
Click on the symbol as in the picture :
Go to "Payment method" from where you can update your payment details :
5. Enter your Credit Card number and click Next.
6. Enter the expiration date and click Next.
7. Enter the 3 digits of the CVV and click Next.
8. In order to confirm the information click on Press OK to continue.