@Fenrispro8 The guide I linked is for how to use the tapestry, it doesn't provide instructions for how to make the specific change you're after. It does tell you how to set choices, etc.
What you want to do to make Alistair a Warden and Morrigan childless (meaning your Warden died), in the Dragon Age Keep, is to open the world state you wish to edit, go to the tapestry, to the DAO section (which is the first section). First you need to go to the companions section, there you need to set 'what happened to Loghain?' to 'Loghain executed by Alistair' (letting him be executed by the warden or defeated in a duel *may* also work, I'm not sure), set 'what happened to Alistair?' to 'remained with the Wardens', set 'did Morrigan have a baby?' to 'Morrigan did not have a baby' (or a human baby to the Warden, possibly, haven't tried). Next, out of the companion section and to the Landsmeet section, where you need to choose 'Anora rules', then to the battle of Denerim section and select 'the warden killed the archdemon'.
Make sure you save and export your world state if you want it to be used when you make a new game in Inquisition.
I *think* I remembered all the choices you need. It has been a few years since I've played around with it.
Have fun 🙂