How we can defined the viscosity of fluid by user defined option.

Dear experts 

I am working on modelling of Hershel bulkley fluid (or genralised bingham). I want define my fluid viscosity as per my experimental data. I have viscosity vs shear rate data but I can not find proper option to use fit my data. I think it may be userdefined but there is no option in viscosity tab of material model. further there are 9 species in drop down list of curve fit variable of viscosity tab. Can I use any species option to define my viscosity vs shear rate data.