How can I change payment setting in App Store to none ?

Create or use your Apple ID without a payment method - https://support.apple.com/HT204034 - "When you use your Apple ID to sign in to the iTunes Store, App Store, or iBooks Store for the first time, you're asked to enter a payment method so that you can purchase items from the store. Follow these steps if you don't want to associate a payment method with your account." - more information: https://discussions.apple.com/thread/8293272?answerId=33067311022#33067311022

Removing a credit card from an account - Change or remove your Apple ID payment information - https://support.apple.com/HT201266 - More information at: https://discussions.apple.com/thread/3251676?answerId=15891166022#15891166022

If you can‘t choose None when you edit your Apple ID payment information - https://support.apple.com/HT203905 - also make sure you don't have any active subscriptions, are set as the Family Organizer for a Family Sharing plan, or owe any money for past purchases.

You can only choose None when you set your payment method up from the iTunes Store, App Store, iBooks Store, or Mac App Store. None is not an option when you use the Apple ID account page to set your payment method.

If you still have problems:

Tunes [Store] Support - Use this form for assistance with account and billing, code redemption, or purchase questions - https://www.apple.com/emea/support/itunes/contact.html

Sign in with your Apple ID - https://support.apple.com/HT204053 - "When you sign in to the iTunes & App Store for the first time, you might need to add a credit card or other payment information to help secure your account."