Hi,
So, let's say you've got a textbox on the screen, and a button.
In the code for the button you can have it change the text in the textbox, the code for that would look something like this
on click do field1.value:"some words" end
So that would make some words appear in the field named field1. Is this what you're trying to do? Apologies if I have misunderstood, I am not sure what you mean by a fixed value here.