As far as I know, there isn't a way to redo quests like that.
HOWEVER, if your reason for wanting to redo it is because you're worried it'll impact your romance with her, don't worry. it doesn't.
You can get a little bit of approval from her, but that's it, and you can get approval from multiple sources. Aside from the approval, it doesn't inhibit or effect your romance.
However, with your previous manual save, try transitioning out of skyhold and back into skyhold, then talking to her again and see if the conversation fires.
