In the guide, you saw “Nag oes,” before “does dim isie i fi…”, and of course, you would use “nag oes” if you were responding to a question to say “No, I don’t need to…”
Although “does dim isie i fi” doesn’t actually appear on its own in the course guide, it can still be used as such when you just want to say you don’t need something. Also note that not every pattern will appear in the course guides, but you will see where such patterns come from by looking at other patterns that are included (like the “Nag oes, does dim isie i fi…” entry).
Remember that the course guides are only there for guidance (if you’re looking to see how the words are written - although you’ve already spotted that “isie” is actually “eisiau”!) and everything in the recorded lessons are (at this stage) introduced and sometimes explained in the lessons themselves (once you get to course 3, some new words will randomly get thrown in without introduction, but all of which will appear in the course guides).