Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
To deactivate Office when you no longer have access to the computer you need to contact Microsoft Help as per Palcouk. When you first setup Office 2013 you would have been prompted to enter the email address and password for a Microsoft Account. That is what you need to reinstall Office 2013. You can change or retrieve your password but it is difficult if not impossible to change the email address. It is just the same as with your Internet Suppler you cannot change the main original email address for the account.
Try here for password: https://support.microsoft.com/en-us/help/12429/microsoft-account-sign-in-cant