Change template

Change template

In a change template under field and form rules. I want to use condition: when Site is A,B and C.
Then I wanna run custom script that sets a specific text in a specific field for my change template.

But i cannot set the conditions for the Sites. 
I choose  "Site" is  but no of my sites can be chosen, why?

So, when user creates a change and uses my template, depending on what site, a text is set to a field.
 

Or is field and form riles the wrong way to solve my issu?