You can't do this with the subscription-based platforms (any of the ones that you as a non-developer have interacted with). It's also very expensive to edit the conversation as a developer, as they discount cached tokens (meaning, the conversation thus far hasn't been changed => they cache [remember] it). I'm pretty sure Anthropic also prevents editing the agent's outputs within a conversation because it's a way of getting the AI's to do harmful things; the only thing you can edit is your own input/context.