App for credit card users?

What's wrong with the bank's app? It will let you transfer money from your savings account to pay the credit card bill.
You can even set up automatic payments if you're worried about forgetting to pay. Or just use your calendar to send you a reminder every month.
There's no need to give an unsecured third-party app access to your bank accounts.

Your bill will tell you what to pay, when to pay, and where/how to pay, it will list where you used the card. I use a credit union with online account viewing so I can see the charges that are pending and complete

It's hardly rocket science. You get a monthly statement with a due date.