Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Dear Cesar,
Good day! Thank you for posting to Microsoft Community. We are happy to help you.
As per my understanding you have mistakenly activated their Office product key with the wrong email address and are seeking ways to reassign the key to the correct email. Please correct me if I am wrong.
If I have misunderstood your post, please let me know. If I have understood your post correctly, this email address cannot be changed by the user. It is only in very few cases will Microsoft change the email address. You will need to contact another Microsoft support and explain what you have done by mistake. I can tell you this was a common problem when Microsoft first introduced Office 2013 and dealers/Geeks installed Office for the customer using their own email address. Only another Microsoft support can change the email address used to setup Microsoft Office. You can try here: https://support.microsoft.com/en-gb/contactus/
NOTE: when you post a question artificial intelligence may respond at first, just keep asking how to change Office Account email address until you get a person. (Sometimes they get mixed up thinking that you want to add an email address, which is different to what you want.)
We're here to assist you whenever you're ready. Have a great day and take care! 😊
Sincerely
Naren | Microsoft Community Moderator