How to validate the flexfield of a page on another page

Content

I created a flex field in the header called type:
This field has 3 options

I choose the type in the header and now I'm going to create items, the system opens another page to inform the items.

In the items screen, I created a new flexfield.
I need to validate if this field will appear according to the type I chose on the previous header page.

From the current page I can get the information from the fields and validate, but I'm not able to validate by the flexfield of the header page.

How to validate the flexfield of a page on another page?