I have a set of data that forms the shape of a log-normal distribution when shown graphically using a scatter plot. I want to determine the equation to a best fit curve in order to perform calculus (differentiation and integration of certain sections). Probability has no relevance to the data and therefore the standard deviation or mean is not of interest. I have tried using polynomial functions to represent the best fit curve (up to the 6th order) but it is not perfect.

My questions:
-Is there any way to plot a trend line (and compute the equation) that has the shape of a log-normal distribution in Excel, when the data has no relationship with probability?
-If not, is it possible with any other software?