In case of a demerger, shareholders in the existing company as on a given record date are entitled to receive shares of the demerged unit. If you held one share of Suven Life Sciences as on Jan 22, 2020 you will receive one share of Suven Pharmaceuticals which will list on NSE and BSE.
As a shareholder, you might want the cost of acquisition of Suven Pharmaceuticals for accounting purposes. You can check this corporate filing on BSE to allocate a cost to your holdings in the following ratio:
This is just an accounting treatment to get the cost of acquisition for taxation purposes. However, to answer your question briefly, you don’t need to take any action as a shareholder. The company will announce a date by which the shares of Suven Pharma will be credited to your account and subsequently listed. You can then choose to stay invested in the company or sell your investments.