How to tie query parameters to page variables

Hi, I need to tie a query parameter on a rest interface to a page variable
This topic says it can be done
But does not explain how - if I go to the rest interface definition there is no option to tie a parameter to a formula or data value, only the option to enter plain text -

I’m a little confused

Ian B.

OK,have sorted this - needed to use the GET logic node instead of UPDATE