I have heard there is a feature in iOS app but it is not currently available to the browser on a regular desktop computer. Must be a feature within the website (not a plugin/addon/integration in the web browser) and available from regular web browsers.
AGI reached per the resolution of this market: https://manifold.markets/ManifoldAI/agi-when-resolves-to-the-year-in-wh-d5c5ad8e4708
If the search past chats feature is implemented in browsers (on different devices) it immediately resolves YES, otherwise resolves NO on the AGI market resolving or if ChatGPT is discontinued or OpenAI goes bankrupt (excepting rebranding) or similar cases.
Searching past chats is rolling out now: https://help.openai.com/en/articles/10056348-how-do-i-search-my-chat-history-in-chatgpt