Hello Ashok,
Thank you for your interest.
The preregistration opens on July 15, 12 AM → 1 PM GMT (Sorry. There is one more step by Pearson VUE team in US to make the calendar accessible by candidates) with the first appointment available on July 28.
Tomorrow (in GMT), you should see the exam listed in the list and be able to select the date and time happening after July 28.