Using Classic Outlook on Windows for personal email, calendar, and contact management
Hey there! Nice to meet you!
To answer your inquiry, you will have to wait for the subscription to expire first or cancel it manually, then purchase a new subscription using the new payment method region.
According to the official Microsoft website: https://support.microsoft.com/account-billing/how-to-change-your-microsoft-account-name-or-address-917b1d70-5915-d04e-243a-a618f96ef1d5
"If you change your billing address, it will only be applied to new purchases. Any purchase in the past or any current active subscription will continue to display the previous billing address. If you need to change the billing address for an active subscription, you'll need to first cancel the subscription, change your billing address, and then repurchase the subscription."
Thank you for your kindness and understanding! Please feel free to let me know if you need anything else.
Best regards,
Darhyl