Note: this answer applies if you're using the desktop version of Quest. I don't know of a way to modify the templates in the online version.
Switching to third person is doable but not trivial. The problem is that the word "you" is used extensively in the templates. Fortunately, all of those templates live in one file: if you're using the English language, then they're in the English.aslx file. On my machine, that file lives at C:\Program Files (x86)\Quest 5\Core\Languages\English.aslx.
I would not edit that file directly. Rather, I would copy it into your game folder and edit it there.
I have created an English.aslx with the pronoun changes. I don't see an easy way to attach files here, so I posted it back on the textadventures site. You should be able to grab it from there: Third-person English.aslx posting. Just copy it into your game folder, and Quest will use it instead of the Core one.