You can modify your personal and payment details in your Billwerk account. If you change your payment method, the new payment method will be used in the next billing period.
Note: For Shopify, please check - How do I modify Koongo subscription? (Shopify)
Modify your billing details
Navigate to My Koongo, log in & select Billing Overview from your Left Menu
Click the Billing Profile button
Modify your payment details
Modify your personal or payment details in your Billwerk account
Select a payment method and fill in the required information. For more info, please check What are available Koongo payment methods?