I know how to do this in Lacerte; you'll have to translate into ProConnect.

In Lacerte, the Screen is 51, titled State Modifications. Then you click on California to get to 51.011, California Modifications. In the Income Adjustments section, where it says Wages [A], you want to click on the button to the right to expand that box, and enter the amount of the HSA contribution. In the Source column, enter an N. The taxpayer / spouse flags are optional.