Having ChatGPT "forget" previous characters / names once it creates new ones

Question about prompting here. I am working on a science fiction novel and I am noticing that ChatGPT includes previous characters from dialogue that are not relevant, even asking it to start new. As an example, I had it re-write a few lines of dialogue, and asked it to “substitute” those character names with the new ones that it created in the same ChatGPT session - but it repeatedly does not follow these instructions. I have tried the key words of “substitute” and “replace” etc. but it does not seem to remember that the new characters it created in the same session needs to always replace the older ones.