If the premise for Marcion's Two Principles (Dualism) is correct; which words in the Bible belong to the Demiurge?

If the premise for Marcion's Two Principles (Dualism) is correct; how does one decipher which words in the Bible belong to the Demiurge from those of the True God? [Marcion of Sinope (Wikipedia)](https://en.wikipedia.org/wiki/Marcion_of_Sinope) Catharism later on also adopted a belief in a form of Dualism and one of their works "Book of Two Principles" outlines the apparent contradictions between the God of the Old and New Testaments; but how did they (like Marcion) discern between the words of the Demiurge from those of the True God? [Cathar Theology (Wikipedia)](https://en.wikipedia.org/wiki/Catharism#Theology)