Nintex Forms 2013 - Conditional text

I am using NINTEX FORMS, no previous experience, and I want to set the value of a tag's text based on the value of a key I send through the query string.

What I am trying to accomplish is something like this:

If(fn-GetQueryString(TipoSolicitud) = "X", "Text1", "Text2")

But this doesn't work at all. Anyone knows if this is possible? and How to do it?

Thanks!