Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Dear Yeva KONDRATIEVA,
Good day! Thank you for posting to Microsoft Community.
I'm sorry to hear that you're having trouble accessing your account. To understand the issue and provide possible solution, May I please double confirm if you are using a Microsoft 365 business email account or a Microsoft personal account such as outlook.com, hotmail.com or live.com?
If you are using a Microsoft 365 business email account, May I please double confirm if the account in question is an admin account or and end user account?
If it is an admin account, May I please double confirm if the account in question is an only admin account or other user has admin privilege in your organization?
May I please double confirm if the account in question is a Microsoft 365 educational account which is provided by your college/institution? If yes, I do understand your query here, but as you are using student account, I sincerely recommend you contact your college/school IT admin to reset your multifactor authentication session from their end in the Microsoft 365 admin account, to be able to add change the phone number that used for authentication and sign in to your account. It's important to note that since we have limited resource and privileges as Microsoft Customer Support, we are not allowed to examine institutional end users account authentication scenario. If the accounts are educational or organization-managed, only the owner or IT staff of that school or organization has the right to manage accounts, including resetting the account multi-factor authentication, allowing account to change authentication methods and changing phone number for authentication method. Therefore, I sincerely recommend you reaching out to your school IT admin or the person who is in charge of managing Microsoft 365 admin center of the school. the admin can refer to this article, to be able to reset the multifactor authentication session of your account in the Microsoft Entra ID admin center, see Manage authentication methods for Microsoft Entra multifactor authentication - Microsoft Entra ID | Microsoft Learn
Thank you for your precious time and kind understanding.Have a nice day.Sincerely,Libeamlak | Microsoft Community Moderator