GitHub Enterprise Cloud allows you to add as many email addresses to your account as you like. If you set an email address in your local Git configuration, you will need to add it to your account settings in order to connect your commits to your account. For more information about your email address and commits, see "Setting your commit email address."
Are you signing in to GitHub.com for the first time in a while? If so, welcome back! If you can't remember the username for your personal account on GitHub Enterprise Cloud, you can try these methods for remembering it.