Do you mean that you want to fit the experimental data by the fitting function in the analysis program "Origin"?
In the analysis program "Origin", you can use "User-Defined Fitting Function."
Some instractions are available on the web written below.
http://www.originlab.com/doc/Origin-Help/UserDef-FitFunc
You need to define your fitting function and perform fitting by the function.
I hope this information will solve your problem.