Hello Than Htut
The reason why you cannot change the default Country/Region from United States to Myanmar on a new payment method is because Myanmar is not currently supported as a payment method for Microsoft products and services.
However, there are a few things you can do to try to get around this issue:
- Try using a different payment method. If you have a credit card or debit card that is issued in Myanmar, you may be able to use that card to create a new payment method.
- Contact Microsoft support. If you are unable to use a different payment method, you can contact Microsoft support for help. They may be able to create a new payment method for you that is specific to Myanmar.
Here are the steps on how to contact Microsoft support:
- Go to the Microsoft website and click on the Support tab.
- Select the Products tab and select Microsoft 365.
- Click on the Contact us button.
- Select the Payments option from the Subject drop-down list.
- Enter your contact information and a brief description of your issue.
- Click on the Submit button.
A Microsoft representative will contact you to discuss your issue and to provide you with help.
Reference Link : https://support.microsoft.com/en-us/account-billing/change-your-country-or-region-in-microsoft-store-5895e006-34f4-10f7-16b1-999e40adb048
I hope this helps! Let me know if you have any other questions.