But really it is very simple to do this. The only thing is that google had not provided the communication about our username.
Actually by default google provides the "bloggeradmin" as the username for our new domain admin.
So, our full username/email is like bloggeradmin@
For example username will be "email@example.com" for domain abc.com
So, now we can easily reset our password of Google Apps if got our user name.
Please go through this link for resetting your password for Google Apps -
How to reset the Google Apps password