Hello SM2444AU,
Thanks for your post in this community.
Based on your post, seems you wants to change authentication contact information for Microsoft365 business user account and for this, please check below steps.
- Login to Azure Active directory admin center via https://aad.portal.azure.com/ > go to Users > All users > select your ex-employee account > now go to Authentication methods, from there you can change email id (if needed you can also change phone and alternate phone contact details from other Authentication contact information).
- Screenshot for your reference:
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If you are not able to access Azure active directory admin center, you need to contact your Microsoft 365 global admin for such changes. At this point, your kind understanding and co-operation will be highly appreciated. Thank you so much for your co-operation .
If we misunderstand your concern, request you to please provide us breif details with your account type (such as Exchnage or any other account) and some screenshot about which things you are trying to change and authentication required, so based on it we will check from our end and assist you further. At this point, your kind understanding will be highly appreciated.
Thank you so much for your precious time. Have a nice day and be safe with good health.
Regards,
Ankita Vaidya