How to get the equation of the plotted curve in Excel?

[median27]

How can I get the equation of the plotted curve (see attachment) without using the trend line?
I've already fitted the random red points using the log-Pearson Type III Distribution (and the result is the blue curve) so I don't need to fit them anymore using any trend lines available in excel. Anyone? Thanks.

 

[tfr000]

Something I do in Excel is to put the parameters of whatever you are trying to fit into some cells. Then, calculate the residuals (the difference <your equation>-<the data>) into some more cells, where <your equation> is calculated from the parameters you entered. Square the residuals into some more cells. Sum them. Now apply Excel's solver to the parameters and the sum of the squares, trying to minimize the sum.