While Re-activating your Tally.ERP 9 you would need your Tally.Net Id and password. And if you forgot the password then you need to reset the password. The process of resetting the password has been explained in previous post on Tally Support Center.
Other options
The other options in control center are manage your ids where you can see all your Tally.Net ids, their status etc.
In change My Profile where you can change the details regarding you e.g. your name and your phone number. The future services like Tally Job and Recruitment and Tally shop would be activated here it self.