Are you using the TurboTax Online product or the Desktop product? I just tried it with the Desktop product and I was able to change the NOL without a problem.
If you are using the Desktop product, go take a look at the Federal Carryover Worksheet (abbreviated as Carryover Wks). Do you see your NOL on line 14a? This is where the amount on line 8a on Schedule 1 (1040) comes from.
**Say "Thanks" by clicking the thumb icon in a post
**Mark the post that answers your question by clicking on "Mark as Best Answer"