Altering a textframe that wasn't created through a variable by getByName

Hello all

Does anyone know how to alter a preexisting textframe within illustrator using extendscript. I can see how to do it after using ".add" and then referring to the variable and altering the contents, but I can't seem to find the answer to altering the contents of a textframe that wasn't created through the script:

I've come across "TextFrameItems.getByName," but I can seem to get it to work. Any help would be appreciated.

var doc = app.activeDocument;

  var Ref = doc.textFrames.add();

var myContent = Ref.contents = "blah";