Could someone suggest how to be most energetic on D-DAY? What can we do from our side that we are the most alert,agile and energetic on D-Day?

you can do meditation before entering exam centre , just search for 15-20 mins guided meditation session on yt plug in your headphones and try to feel light and calm.

on D-day you itself you will be at your full focus but with a feeling of pressure/anxiety/stress which you cant control.