TimeRex does not allow you to change the email address on your account.
In order to work with your new calendar account (email address), you will need to register a new TimeRex account again with a new account (email address).
From the TimeRex TOP page, go to "Free Registration" and login with the appropriate account (email address).
For information on how to register a TimeRex account, please refer to this support page.
If you have a TimeRex account that you no longer need, you can delete it.
For information on how to delete your TimeRex account, please refer to this support page.