Are you trying to correct the entry on the review screen? Instead, go back to the section of the TurboTax interview where you originally entered this number, and see if you can change it there.

Yes, but it's already 104 in the relevant section. That's the rub. It tells me it's not 104, inserts 104 into the text field (presumably pulling that value from the section), and then wants me to change it to 104. It's as if there is a floating point rounding error and the 104 I see on the screen is not strictly equal to the 104 I originally inserted into the form.

104 is my new least favorite number. 😕

At this point, you may want to contact TurboTax support: https://support.turbotax.intuit.com/contact/