Can't edit value for existing reference value

Hi, trying to follow:

Reference Lines, Bands, Distributions, and Boxes

I can't edit existing reference line:

1. The first thing is that Tableau stopped to display it

I have no idea why...

But I can see "non visible" reference line named "Target":

What is the right way to change value for it? Right now it's 20, I want 24.

I'm fine with deleting it (have no idea how to do it) and creating new one.

Please help.