1st Step: Login to your bsport account.
Go to this web page: https://backoffice.bsport.io/login and log in with your email and password.
2nd Step: Change the payment method.
Once logged in, click on 'Subscription'. A notification appears to inform you that you have a subscription without payment method yet.
Click on "Modify" to change your payment method or on "Add" to fill it in.
Fill in the payment method's informations.
Click on the saved payment method to highlight it and click on 'Bill'.
Your subscription will now be billed on with this payment method.