Sales tax

I bought a car this year and want to deduct my sales tax. The form just became available so I went exploring and it took me to a place to enter my cars price and sales tax. I didn't have the information available at that moment so I quit the program to continue later in the day. Now when I go into the sales tax deduction I can't get to that place anymore, it just wants me to enter my total sales tax paid. How do I get back to the entry for the car?