After my tax file been reviewed, one blank is asking how much tax I want to pay now, and I think I might misunderstand it and get it wrong, how can I go back and fix it?

 

Get your taxes done using TurboTax

Since you cannot make a "partial payment" using the TT system I have no idea where you are.  Until you actually efile by clicking the big orange button in step 3 of the FILE tab you can wander anywhere you wish ... so click on any tab to return to any section and run it again to make any kind of changes needed.