Sonal Srivastava Mam, Firstly, you should have a regression equation to calculate the CC50 value of herbal extract. For e.g. the equation is y=ax+b (Put 50 in the given equation in place of 'y' and solve the equation. From here you got the value of 'x' which is CC50 of your herbal extract.
there is a method of converting the data to a regression correlation but it not correct, you should use special program to calculate C50 (graphpad) is the best