fitting data to a lognormal distribution custom equation option

Hi, I am having some trouble regarding fitting a dataset (2 dimensional data (x,y)) of mine to a lognormal distribution. It is to my understanding that I could create a custom equation in matlab and perform a fit to the the data with a lognormal equation. Additionally that the program would be able to tell my sigma and mean values and it would be able to tell me how well of a fit I have via a rmse/rmsd calculation. If anyone knows how I could perform this fit I would appreciate the help.