Chi square test on a custom fitting function

Hello everyone!

I wrote a code in order to do a fit test with a custom function (code below)

%MODEL 1 Dose = a*netOD + b*(netOD)^3

x = netOD_average.'

y = dose

model1 = fittype({'x','x^3'})

fit_model1 = fit (x, y, model1,'Robust', 'Bisquare')

plot (fit_model1, 'black', x, y);

Now I'd like to make a chi square test to find the goodness of fit value. I've already search and try with the chi2gof function but I don't know what to use it.