Enter your code Z on the "box 20 screen". You don't need to enter an amount on that box 20 screen, but you do need to click Continue after you have entered the code Z. The next screen is "Describe the Partnership" and the the next screen is "We see you have Section 199A income" and then you should get "We need some information about your 199A income", followed by "Let's check for some uncommon adjustments". When you get to those last two screens, when you check the box on a line, other boxes will "open up" to enter the amounts from your Section 199A Statement/STMT.
Note that Unadjusted Basis of Assets amount goes on the "....has UBIA of qualified property" line.
To get back to the K-1 summary screen and find the Schedule K-1 to edit, click the "magnifying glass Search" icon on the top row, enter "k-1" in the search window and press return or enter, and then click on the "Jump to k-1" link to find the K-1 you need to edit.
Here are screenshots of the "We need some information about your 199A income or loss" and "Let's check for some uncommon adjustments" screens where you enter the information from your K-1 Section 199A Statement/STMT: