Hey,
Scuba diving is definetly a must do activity. It takes about half a day but its an inexplicable experience. Other than that you have riding the cruise from one island to the other, boat ride and snorkeling.
https://www.tripoto.com/andaman-and-nicobar?params=%7B%7D check this link for details on everything you need to know about the island.
Hope this helps.
Diving can be a good solution. Also, think about windserving or things like wing foil - https://easy-surfshop.com/do/cat/foil/WING-FOIL
It can give you great emotions and you can have a very active time in this place.