Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hello Hocine1,
Thank you for your contributions to the Microsoft community. We are happy to help you!
Based on your description I understand that you cannot change the country set for your trial subscription to add your credit card. Please note this is an expected behavior, the country or region of your subscription cannot be changed. In this case you may have to create a trial subscription registered to your preferred country. For more details on this please see Change your organization's address and technical contact in the Microsoft 365 admin center - Microsoft 365 admin | Microsoft Learn.
We look forward to hearing from you. Thank you for your cooperation.
Best regards,
Simbarashe | Community Moderator