Hi, I'm John! I will help you with this.
Microsoft ties your billing currency to the region where the MS 365 subscription was first purchased, the best way to update it is to cancel your current subscription, change your Microsoft account region to your new country, and then repurchase the subscription there.
This will ensure your billing matches your new local currency and payment methods.
"Cancel a Microsoft 365 subscription" https://support.microsoft.com/office/cancel-a-microsoft-365-subscription-46e2634c-c64b-4c65-94b9-2cc9c960e91b
"Update a Microsoft account payment method" https://support.microsoft.com/account-billing/update-a-microsoft-account-payment-method-2ca44141-c10d-a693-7ea6-3a22f5213283
I really hope this information is helpful! Let me know if you have any further questions or concerns.
Regards,
John J.D.