You cannot change the payment method you initially chose when signing up. To change the payment method, you need to cancel the subscription first then subscribe to the channel again.
Please visit the channel page to unsubscribe from your monthly channel subscription. After canceling it, subscribe to the channel again with the new payment method.
NOTE:
If you subscribe to the channel again in the same month, you will be charged again for the same service period. To avoid paying twice, we recommend unsubscribing at the end of the month then re-subscribing again the next month with the new payment method.