Simply enter your preferred name in the email field.

Office 365 Setup Documentation
To set up Office 365 Pro Plus, go to www.office.com and log in with the provided email address and password. You will be asked to change your password on first login.
After logging in, you will see the "Install Office" button in the top right corner. Click on it, then click "Office 365 Apps" to start the download. Once the installation is complete, open the installed application and log in with the provided email and your new password to start using all Office applications.
First login is guaranteed. Any issues during the first login will be resolved free of charge. No compensation can be provided for issues occurring after that.