How can I change the country on my Apple Account?

Hi,

I am Kornkham from Myanmar. I used to create my Apple ID in Malaysia and now I am back to Myanmar. I would like to add my payment method which is available in Myanmar. But in the billing address, I couldn't find Myanmar to choose the country. Can anybody help me with this?

Thank you.

[Re-Titled by Moderator]

Original Title: Myanmar Apple ID