If you want to make purchases or update / download apps, including free apps, you need to have a payment method on file.
You need to tap Continue
Tap Continue and sign in to view 'your' billing information.
You need to -> Sign in to your Apple ID account page and edit / update your Apple ID details.
https://appleid.apple.com
On the Sidebar click Payment methods -> then tap Payments Methods and tap Manage payment method.
If you don't have a credit card or don't want to use a credit card, you can also use your Apple ID balance as payment method, see -> Add money to your Apple ID balance
Add money to your Apple ID balance – Apple Support (UK)
- if you want to use your Apple ID balance, you need to set your Apple ID balance as your default payment.
If you update your payment method or add funds to your Apple ID balance, It would take about 1 to 3 business days in order to process.
If you're still unable to update your payment method, Contact Apple Support.