To make a payment from the app, you would click on the menu in the upper left and select Payments or click Pay Now at the top of the screen next to the balance if you have one.
You'll see this screen if you have already set up your online payment method.
Click "Make Payment" at the bottom to complete your payment if your balance is correctly listed.
How to Change the Amount Paid
If you need to change the total amount that you're paying for, click on the pencil next to the amount number (circled in red above). Once you're finished entering the amount, click on the blue box with the check mark (circled in red below) to save it and select "Make Payment" at the bottom.