There are two ways to change your credit or debit card information if you have an unpaid invoice

In app

Go to the 3 lines at the far right. There you can see your subscriptions, receipts and what is unpaid

To change your credit/debit card go to unpaid and click on pay. There you can remove your old credit/debit card information and fill out the new one. Then press pay.

In computer(browser)

Go to the website you bought the course/training fee f.x"nameoftheclub"

Login at the top right corner and in the top right corner you can see my invoices and my subscriptions. In my invoice you click unpaid or the subscription you want to add your new card information. There you fill out your new card information and click pay.