Deductions & credits

I don’t know what I am doing wrong. 
I signed into TurboTax. 
I selected my 2018 return and amend.

I carefully followed the instructions. My federal return changed to ‘0’, and my state return changed to ‘minus $319’ (although I had received a refund).

When I attempt to enter new figures to amend return, I am cycled between ‘update’ and ‘continue’.  I am given no opportunity to amend the figures in my return.