How to solve billing method from iphone

If you have a billing issue, see this, If your payment method is declined, or you have a billing issue with a previous purchase in the iTunes Store - Apple Sup…

If you are attempting to use mobile billing for iTunes, then see this, Set up mobile phone billing as your Apple ID payment method - Apple Support

Not all areas or all cellular carriers support mobile phone billing, so you may need to check with your carrier after checking the support document I linked.

What do you mean by “solve”?

If there is no iTunes Store for your country, then Apple can’t offer you anything in that country.

You may express your wishes through the feedback page.