How do I get back to interview questions for the HSA? I wan tto see if I contribute after tax how much my tax payment will decrease

Type 'hsa' in the search box at the top of the TurboTax screen and use the 'jump to hsa' link to go directly to that section of your return.

But that doesn't get to the question did you contribute money after tax?  I am assuming I said no on it before but I want to change it to yes

No it doesn't go directly to that question, but it is the starting point.  That question is in that section of your return.  You just have to go through some screens to get to it.