BH Curve as function of normH and T

Hi,
I'm study the induction heating of a billet and I'd like to implement a BH curve as function of normH and the temperature. I have an analytical formula for that where I compute the normB as function of normH and T. This analytical formula is not inverse and I can't invert it. In order to reach that I add a BH curve in the material propriety where I report my formula. when I lunch the solution the software answer that doesn't know normH that in principle should be an input factor. So seems possible to give normB as input and extract normH but not the opposite that it my case. There is something of wrong in my procedure? Can someone help me to solve that problem?

Many Thanks

Best Regards,
Nicola