In a project with pure Cuba I have managed to do it, since the “Controller” screen allows me to edit Java code and others, but in Polymer I do not know how to do this.
Yes, thanks for the answer, it became clear to me.
I take this opportunity to ask you a different question and something simpler, although I do not know how to do it since I am a newbie. I want to have a button with an action that when I click on it, I open another screen that I have in Cuba (I speak of Cuba, I leave aside Polymer). That is, with a button can open another screen created by me.